You can tell a watercolour painting by just looking at it! Watercolours tend to be lighter because of the water required. Watercolour paintings are light. Notice it!
You would have to go to an art gallery and talk to one of the managers there and they will be able to tell you if you show it to them. Pablo Picasso did not paint in water colours anyway, he painted...
Experiment! Try mixed media- sharpies, pen, charcoal, etc. over/together with watercolor! Also, I find watercolor pencils are very useful in the creation of watercolors. Have fun! :D
Buy a jeweler's magnification eye glass (10X power is good), and look at the print through the glass. If you see dots, instead of brush marks, then you have a print. If the you see brush marks, then...