P.m.t.t. Mystery Stamp

Here's another intriguing mystery stamp. This one is printed in yellow on white showing what looks like a maple leaf, and (barely visible) letters S, C, N, and M in each corner. Then it has initials "P.M.T.T" and "$3.00" overprinted in black. Then there's a date of "Juin 1957" handstamped in purple. And finally there's a manuscript cancellation, probably with ball point pen. My guess is some type of receipt stamp for union dues or a special event, possibly from Canada (maple leaf) and more specifically from Quebec or New Brunswick (as the date is in French). Any ideas?

I cannot find them in Van Dam, but I have a feeling that they are from the Province of Manitoba, and possibly some type of telephone and/or telegraph revenues. Or possibly some thing else that T.T. might stand for.

Thanks revcollector:
That's an interesting suggestion, something like Province of Manitoba Telephone and Telegraph. Although the French date seems a bit of a stretch for Manitoba, and $3.00 to send a telegram in 1957? But who knows?

Other possibilities I've considered (and rejected):
PMTT: Professional Musky Tournament Trail, professional anglers' group formed in 1998.
PMTT: Prahran and Malvern Tramways Trust, tram operator in Melbourne, Australia from 1909-1920.
PMTT: Perceived Mean Travel Time, term used in transportation and traffic theory.
PMTT: Project Management Tips and Tricks, discussion group
PMTT: stock market symbol for PAMET SYSTEMS INC
PMTT: Precision Mobile Tank Tester is a combination liquid level and ullage testing system specifically designed to detect leaks in large fuel storage tanks.
SCNM: Southwest College of Naturopathic Medicine, located in Phoenix, Arizona
SCNM: Sealed Container Notorious Monster (SCNM) are a series of Campaign related battles taking place in the three Beastman strongholds located in La Vaule (S), Beadeaux (S), and Castle Oztroja (S) (online gaming).
SCNM: Soccer Club of New Milford (Connecticut, USA)
SCNM: Singapore Coins and Notes Museum
SCNM: State committee on nationalities and migration

As you can tell this is driving me batty!

Societe General N*** Montreal?
Could the C be a G?

Here's a blowup of the corner from another such stamp. Looks like a "C".
Maybe Societe canadienne..?
Or Syndicat canadien...?

I searched the Lovell Montreal directories for 1957 and 1958 for companies/organisations starting with Societe:
1957:
http://bibnum2.banq.qc.ca/bna/lovel...957_1519.pdf
1958:
http://bibnum2.banq.qc.ca/bna/lovel...958_1613.pdf

And starting with Syndicat:
1957:
http://bibnum2.banq.qc.ca/bna/lovel...957_1539.pdf
1958:
http://bibnum2.banq.qc.ca/bna/lovel...958_1635.pdf

Closest match would be Syndicat National des Charpentiers et Menuisiers de Montreal, but that would require the initials in the corners to go up and down, instead of across. But it's an interesting lead...

I suspect you may have to go further back than 1957 as perhaps the SCNM changed names prior to that and that is why it is overprinted with the new company initials? Of course this is pure speculation. Of course, Seeing that it is a C, it coudl be Sosiete Cooperatiive. But I see by your link the only one in 1957 doesn't match.

There's also the possibility it's a Union dues stamp, meant to be pasted in a booklet and shown to the Union treasurer upon request. There's a wide variety of German cinderellas with 4 or 5 letter abbreviations, and many have been identified as membership stamp-receipts.