My wife and I are separated for 7 weeks now, without any major contact. Two weeks ago it was our anniversary, and I also had the doubts you are having.
I decided to send a short SMS message where I hoped she was feeling fine and where I wished her a good evening.
She didn't understand it because she probably didn't remember it was our anniversary (she's not very good with dates). I had to send her another email explaining and the experience wasn't very good now that I see it in perspective.
So, it didn't work for me. Before you take the decision to send something, make sure you know your wife knows it's the anniversary, that she won't feel emotionally pressured by it and that you aren't either too vague (like I was) or too emotional with your message.
Good luck, regards.
Me: 36 Wife: 33 Together: 09/2007 Married: 03/2010 I love you but...: 06/2011 Separated: 06/2011 Rebuilding: 11/2011