simple macro to send a whisper to the GM?

I'm trying to put together a simple macro that I can click to fire a whisper to my GM.  Once I click the macro, I'd like it to open a dialogue box that I can enter the text of my whisper into.   I've googled how to do this and gotten some conflicting information, and I'm not able to make it work.   I'm sure this is very simple, but I haven't buckled down and learned the macro syntax yet.   Any help appreciated.  

I have a very simple on that I have set up as a token action for each player. /w gm ?{Message}

perfect.  Thank you.   Good grief.  My problem was simple.  I was putting the macro text in the macro name field instead of the correct place.  Ugh.   Thanks for the help.