Insert date

Hi!

Recently, I came across the idea to bind a key to insert the current
date, just like I bound keys to insert things using "stuff".

However, I tried :bind d exec ! date +%Y-%m-%d. That almost works like
expected. I couldn't figure out exactly, but screen adds some strange
control character before or after the command.

Why doesn't this work? How do I realize to insert the current date?

Julius