$2 Bill - Strange serial number (or not)??

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I found this $2 Canadian Bill, Serial #UM3102082 from 1974.  Almost mint condition.  Looking at serial numbers on other $2 bills, they all have 3 letters at the beginning.  I noticed that this bill only has two letters "UM".  Is this normal?  Thanks.

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The 2-letter prefix is normal. it was used on 1969-1975 Scenes of Canada notes, until 1981, when the 3-letter prefix replaced it.