My co-workers often ask me "are you busy?" before asking for help or discussing a problem. I find this question hilarious: If you answer yes then you are a bad employee because you are unavailable and can't help the team, if you answer no then you are a bad employee for not having stuff to do.
Usually the answer is "not too busy, what's going on".
What is the best way to communicate that you are working, but have time to help?