anything over 100mW where you didnt cash really much extra is multimode. at least if you arent sure about it, you can be sure its not singlemode..
worse than multimode? multi-emitter.. but then those wont begin at 300mW i guess, and again, you will know about it when you have your hands on one!
there is that datasheet for the gb diode, you will find the nm in there. dont have the pdf here, google the diode's name, and you should find it.