Malcolm -- I thought my magnifying glass must not be working when I saw your image of the China General Omnibus token with hidden letters T - A - M. So I went through my collection again very carefully. This 5 cent token, and the 2-1/2 cent token in the same set, were issued in 1926. Previously, a similar set was issued in 1924 in values of 1, 2 and 3 cents (with Chinese characters for the values cut-out). All three value of the 1924 set have the letter M in the D of GOOD and in the D of LTD. The 2-1/2 cent of 1926 has an M hidden in the first O of GOOD. The 5 cent, however, comes in at least 5 variations:
1) AM hidden in 2nd O and D of GOOD no hidden letters on the other side.
2) AM hidden in 1st O and D of GOOD and M in D of LTD.
3) AM hidden in 2nd O and D of GOOD and M in D of LTD.
4) AM hidden in 2nd O and D of GOOD and M in C of CHO.
5) TAM hidden in 1st and 2nd O and D of GOOD -- this is your piece -- a new discovery -- and I would like to know what is hidden on the other side.
When I only knew of the letter M, I suspected it might stand for the name of the company which made the tokens. But now that there are three letters, and we know the order is TAM, I suspect those are the initials of the engraver. According to Woodward's Coins of Shanghai, these tokens were made in the USA. There are many similar transportation tokens used all over the USA around that time. I wonder if any of those have hidden letters? Some of the USA pieces with this scrollwork background were made by S. G. Adams Co. of St. Louis. They made the St. Louis bus tokens of this style. Perhaps TAM worked for Adams? The first person to report these hidden letters was Elmer Randall, who contacted me about them in 1998.