|photo altered to obscure phone number*|
Curtains in the window? Not recommended. If you want to pretend you're selling tropical fish, you might want to consider an aquarium in the window—maybe even with tropical fish in it? At least put some photographs up, something passersby can look at. Specifically preventing them from looking in, having your window display essentially be a window disguise, risks arousing suspicion: the opposite of your goal.
The name, too, is important. Let's say your tropical-fish store is a front for a drug-smuggling business, or a brothel—whatever your thing is, doesn't matter. The problem with a name like "Koran" is that it in post-9/11 America there's this suspicion of Muslims that turns anything that sounds like a reference to Islam into kind of a red flag—again, the opposite of our goal. So a curtained establishment with a big, red "KORAN" sign is not exactly flying under the radar, even if you do put the words "TROPICAL FISH" up there, too.
On the other hand, if this is in fact the headquarters for a terrorist cell, then you score points both for boldness and possibly even for a kind of double fake-out, the "so obvious it can't possibly be so" gambit. So:
FINAL GRADE: C-
* ...because I am kidding. (Is this joke OK? I DON'T KNOW.)