Cleaning Grill Cloth

I cant blame anyone because I didnt see it happen, but there seems to be finger marks on my grill cloth on my thiel 1.6's. Right in front of the tweeter, all is fine with the speakers no problem there but depending on the angle you look at the speaker, you can see it.

How should I go about cleaning the grill cloth it "looks" like maybe a little one may have had wet or sticky hands that innocently touched the cloth.

Any suggestions?