Balk?

[UmpJM]

MrUmpire,

Could you give me a cite please, because I can't find it.

The only one I can find says that when he's on the rubber he shall take his signs from the catcher.

As the rulebook language sugggests, this is to prevent the pitcher gaining an unintended advantage over the batter or runners by engaging the rubber and immediately "hurrying into the pitch" without pausing to take signs:

Official Notes - Case Book - Comments: Pitchers may disengage the rubber after taking their signs but may not step quickly onto the rubber and pitch. This may be judged a quick pitch by the umpire. When the pitcher disengages the rubber, he must drop his hands to his sides. Pitchers will not be allowed to disengage the rubber
after taking each sign.

The one you're talking about that prohibits the pitcher from taking signs while he's not on the rubber I can't find in the rule book or any interpretations manual.

JM