They will say "aquatic" or "semi-aquatic" on them - you can use the semi-aquatic in emersed or riparium setups, just not submerged in a tank. At my store, it'll say it on a big green circle on top.
I'm not near any good LFS, so I find these to be a decent option. I picked up a package of cryptocoryne once, and actually ended up with more plantlets than I knew what to do with. You just have to be careful and pick out a healthy one, and of course do your research beforehand to make sure you can support the plant once you get it home.