I'm pretty sure I'm going to be hated for saying this, but it really gets under my skin when people call themselves a "single mom" if they're divorced or if there is anyone acting in the second parent position. "Single mom" to me means that they're doing it all themselves, when in fact, they may be co-parenting, just living in separate homes.
If the point is to let eligible mates know that they are available to date, then just stop at "single". If the point is to let people know that you're a mom, then just say so.
I'm bitter because my somewhat irresponsible niece is a "single mom" who expects to be congratulated for doing 'such a great job' when in fact, she's leeching off her parents due to her less-than-ideal life choices.