You can do a few things, but really there's almost no way of knowing what strain it is, especially if the seeds are from a random bag of buds.

-Whenever they flower compare the buds to pictures of other grows on the forum.
-The shape/size of leaves may indicate the origin of the strain. (Fat vs Skinny, etc..)
-Note the floral undertones, as if it smells like fuel it may be some sort of diesel, etc... Smell and taste are great indicators for certain varieties.
-Ask the person where the bud came from which strain they've been growing/acquiring.
-Check out all the "Big Book of Buds" series, as there's hundreds of strains and pictures.
-Once the grow finishes, you can post a smoke report and include pictures of the plant growing as well as pictures of the finished product, include what it tastes like and smells like. At that point other members (who've grown many strains) might be able to take a few guesses.

I wish you good luck figuring out which strain it is, but really don't even worry about it if you can't determine the strain. Just enjoy the whole cultivation process and get legit seeds for round 2.

Hey Swell! Thanks for the reply... For some reason I can't upload a pic.. Yeah I do know it is an Indica. When I have taken sun leaves off I can smell it and I know the smell... LOL well your right... Bring the smoke!