Also, when they're cleaning the glass, their mouths will be that of a normal algae eating snail, but way smaller. It will rasp at the algae like trochus, turbo or any other common snail. Some will have a pinkish-redish color to their foot, which some people will confuse them as a whelk, others more opaque or whitish.
Once they start reproducing, you can easily trade or sell them to local reefers. You'll be surprised how quickly their numbers increase. For me, they're among the top 5 snails to have in a healthy, diverse CUC, way under-rated in my book.