Chicane-We just signed orange, but then, mandarins are pretty much all we gave him in that category, so it wasn't confusing. If you do regular oranges too, the I love the baby orange idea!
Amy-I started signing to DS at 6 months and at 13 months he finally signed back....We did the standard eating signs (milk, all done, more etc) but once I knew he understood them (even though he didn't sign back...like he would come crawling over when I signed milk, or open his mouth when I signed more) I started adding more signs. I found the first sign he signed back was something really important to him, which happened to be "outside". For my DD we started with the same 3 eating signs, but the first thing she signed back was kitty. Either way, once they got going it snowballed and they were both signing a dozen words within another month. Good luck! Nothing is better than finally being able to communicate!