ok, as for chemical\other yes.
first, print out the logo you want\need from your computer at the correct size IN REVERSE. then, using some rubber cement- glue this image EXACTLY where you want it to be, FACE DOWN on the BACK side of your plexi. when you look at this image thru the front side of the plexiglass you should be able to see it correct.
ok, then mask the entire thing off with some clear duct tape. *clear for a reason* (thicker layers = better)
ok, now shine light under the side withuot the image (so you can see thru the paper and clearly see the image, and using an xacto knife, cut out (CAREFULLY) the image that has been printed... you are now cutting the area that will become frosted. so make sure you know what you are doing.
now, rent or find a sandblaster, and shoot the area you cut out *MAKING SURE ALL OTHER SURFACE OF THE PLEXI IS COVERED or else you will get scratches and everything.
this will 'sand' down the surface you cut out and make a pretty logo.
rip off all the tape and VOILLA!
OR
get a vynl negative\reverse cut out on a vynl plotter and stick that wherever you want, then cover, then sandblast, then the same results.
it is all quite tedious, but the results are fantastic.
or you could spend a crapload of money and have some sign company use a lazer etching machiene to do whatever design\cuts you need to your exact specifications.
good luck mang =D
