Can anyone tell me how I can tell if a piece is carnival glass? Is there any writing on it that I can look for?

There are some good reference guides out there. Different companies made different patterns and marks can often be the key. Some, however, are unmarked and if you're not all that familiar with carnival glass you ought to have an antique dealer look at it. There are lots of repros on the market.

Here's a lot of info on carnival glass.
www.ddoty.com