Decode this rebus, said to be posted in a tavern:

language/english/rebus New

New entry, edited from material collected for the archive and not yet in a released version.

Problem

Decode this rebus, said to be posted in a tavern:

If the B mt put :
If the B . putting :
Don't put : over a - der
You'd be an * it

[ Editor: problem statement reconstructed from the source, which gives
  only the rebus with its reading. ]

Show solution

If the B mt put :           (If the grate be empty put coal on,)
If the B . putting :        (If the grate be stopped putting coal on.)
Don't put : over a - der    (Don't put coal on over a high fender,)
You'd be an * it            (You'd be an ass to risk it.)

Allegedly from Mrs. K's Toll House Tavern in Silver Spring, Maryland
(Word Ways, 12-51, February, 1979)

[ Editor: see also the amUous Mind Puzzles in the entry "web.sites". ]