Why do some model names use "MKII"?

Ok I am going to show my ignorance here. It seems very common for an amplifier to have a model name with a MKII reference. It seems to designate either an upgrade or a special version of a previous model. Can anyone educate me as to the origin of this nomenclature? I am guessing it is a tribute to a classic guitar amp, but I'd love to know for sure.
It is just an abbreviation for the words Mark Two, (meaning version number two). To be honest, I don't think it has anything to do with guitars at all, but merely standard production nomenclature.

My two cents worth anyway.
It generally means that the manufacture didn't get it right the first time :-)
Or happy MKI owners will have a chance to be happier, where they might otherwise just stick with what they already have.
I like Brf's response!
Some manufacturers tend to do this more than others.
Other just come out with a new model. Either way, it is the best way to raise prices!!
Like Manley just raised prices. They would have been better off to do a tiny bit of 'upgrading', then rename the product with the price increase. i guess they are just too honest!
Actually, one mkII took some parts OFF! the mkII of the famous Audio Research Sp-10: the mkII removed a device sitting in the middle of the circuit board, so you knew if the original was upgraded because the gizmo was NOT in it's spot on the circuit board. (I know because I owned a SP-10 upgraded to mkII) the other few parts changed really were not enough to warrant a name change, so the mkII designation for the Sp-10.
Worrying abot it is silly IMO. If a company is willing to do constant research to better thier products, why criticize them? Some companies make a product and then that is it. they stop dead. it's done, who cares...
Others continue to work on them, some do not even tell customers (like Bryston) that later serial numbers have 'better' parts or features, and others do.
(The Bryston I know of was a transformer upgrade ala Stereophile review of 7B-SST2 amps.. and that is not the only part that they have made better and just add it in the production. (Bryaton is not 'hiding' anything, they also are not advertising it either.)
Like kurt-tank said , it's just a newer version . Some call it mark 2 some add a letter or number some manufacturers give it a new name but it all means the same .
This also opens other doors, Upgrade your MK1 to a MK2. You really won't know what you were missing till you hear a MK2 whatever. Now there will be slight sonic difference between an MK1 upgraded to a MK2, than a brand new Full MK2. They might even offer a Signature Series MK2 for only 5k more. What a crazy hobby.
I think that many do pursue the ceaseless pursuit of improvement, sometimes parts become unavailable and new one's must be used. However, I do think that the basics of great preamp and amps design is pretty well figured out and has been for many years, though there have been some improvements in passive parts. So yes, there is a quest for improvement, but there also is a very power marketing reason for new models on the showroom floor.
Mark II was the second king of France.
After MKII, sure to follow will be Ultimate, Special Edition,
Signature Edition, Reference Signature, and finally Master
Reference Signature Edition MKII followed by the new MKIII.
"Mark" is the term con men use for their victims.
Pubul57: You forgot "Statement"
Interesting question, though not, by any means, restricted to amplifiers (see cars, vaccuum cleaners, etc).

A little search on the etymology of the phrase didn't yield a direct answer, but here's a guess based on what I saw.

One archaic meaning of "mark" is boundary. "Mk II" would suggest an expanded boundary (presumably for performance) of the "Mk II" device in question, relative to the MKI. Similarly, the "Mk III" would push the boundary beyond the "Mk II".

Just a guess.

We have used this nomenclature. Our first lineup did not use the 'Mk I' tag; that got applied after the Mk IIs were introduced. So the Mk I lineup went for about 17 years.

The Mk II was the most significant update that we had developed during that time. In it, we went from miniature tubes to octal tubes, so to update older amplifiers required us to do a lot of chassis work to accommodate the larger tubes. None of the prior updates needed this- nor were those updates as significant- hence Mk II.

The Mk II series went for 9 years and in 2005 we introduced the Mk III series. What is nice about this approach is that it allows us continued refinement of the basic models, for example our flagship preamp, the MP-1, has been in production since 1989, although considerably updated since its introduction. This approach allows us to support the legacy products in the field- we can update any of our prior amps or preamps to meet the latest spec, and when we do that we reactivate the warranty.
I do trust products that are well sorted overtime by gradual evolution of an original idea that was good to begin with (CAT SL1, Merlin VSM, Atma M60s, Vandersteen 3A) for example, rather than product lines that change dramtically every 3-4 years, claiming new technlogy or circuit breakthroughs. The "evolvers" tend to have gotten it right the first time in the basic conception, and slowly over time there are real imporvments in passive parts that lead to refinement of the original, as opposed to a wholesale rethinking. I never though about that much, but the products that I own and have most enjoyed are coincetantlly those that sort themselves through time with minor improvemnts to the original.
It means you don't have the oldest version but a new version is forthcoming.