Glass "DEATH TO YEGG'S" item

[Yankee]

I have acquired this unusual item of glass, and would like input as to what you all think it was used for.

It is a Robins Egg blue with color variations through out. The markings are raised and read as follows:

DANGEROUS

DEATH TO YEGG'S
PAT.MAR.7-1922

BURGLAR PROOF LOCK
COMPANY

U.S.A.

It measures 4 3/16" at the top from left to right.
4 5/8" top to bottom, and 2 3/16" left to right at the lower part with the writing on it.
It has a cast hole of just 15/16" and is 1 9/16" high at the top and 1" at the bottom.

On the under side it has a "shelf" that is very crisp and appears to be made to hold an insert of some type.

OK, now what was it used for ? Feel free to make wild guesses...that's what I've been doing.