It stands for Will Help in Return. Someone usually puts this in when they are asking for advise, saying if you help me, he will help you with any questions.
I didn't know either. So thanks to Rhino for asking and to Smooth for answering.
A baseball fan has the digestive apparatus of a billy goat. He can, and does, devour any set of diamond statistics with insatiable appetite and then nuzzles hungrily for more. ~Arthur Daley