Is it inappropriate for a single male to send a birthday card to a woman who has gotten married, even if there is / never was any romantic interest?

I decided not to do this. It isn’t prudent, and I feel it could cause some uneasiness or problems.

I am in a committed relationship myself, and I never had any romantic interest in my friend from long ago. I know she would be glad to hear from me, but when someone is married, this might look suspicious.

So there. I answered my own question? Still, I am uncertain about this, maybe because I am in a very ambivalent time right now and feel a need to connect with people from my past. Especially those who might want or need to reconnect as well with friends from earlier times.

Please comment on this, or on whether, in general, a single person can send a card to someone of the opposite sex who is married, even if there is no romantic interest.