Depo and Pregnancy

I know depo is pretty darn effective but just a question if I did somehow end up pregnant there's always a slim chance how can I tell? I don't get my periods with the depo anyway. I've never been pregnant but most women in my family didn't get morning sickness so I won't even be able to tell from that. What are some other early signs? I just want to know so I can be prepared if something does happen to come along. I don't want to end up on "I didn't know I was pregnant"