What you have is a portion (not the entire) meter imprint. The fact that it reads "P.B. Meter" identifies it as being from a Pitney Bowes Postage Meter, which was (and still is) one of the most common postage meter companies.
Although not an exact copy of yours, the entire imprint should look like this:

The style is typical of Pitney Bowes equipment in use during the 1950's and 1960's.
There are meter collectors who will "flyspeck" these and be able to tell you what specific Pitney Bowes Meter Model used this imprint. If you closely compare your example to the one I scanned, you will note the lettering (particularly noticeable in the words "P.B. METER") is slightly larger in your example. Some of these seemingly minor details can actually identify the equipment and dates they were in use.
Likewise, there are people who have accumulated databases of the meter numbers and can provide detail on the specific user, too.
There is even a Meter Stamp Society dedicated to the art of collecting these specimens. Here's the link:
http://www.meterstampsociety.com/terms.htmlIt can be a nice side collection, but I wouldn't get your hopes up of finding anything terribly valuable amongst them.