This check was deposited in the 1930s, and it was issued by OCBL (an old bank in Singapore). The checks issued by this bank had an interesting feature - an obfuscated pattern printed on the back of the check.
All original documents about the design of this check have certainly been lost, and there isn't any later documentation that addresses the usage of this "pattern", but some agree that it might be an example of steganography, so that security personnel could put a cardon-grid-like card on the top of the pattern and thus reveal some information to help verify the check's authenticity.
My question is not about deciphering the secret based on what it has to offer as steganography, but focuses on the following directions:
Is this pattern really an example of steganography? Has any bank or financial institution ever printed a similar type of pattern on their checks before? If so, what is it?
If it is steganography, what information could be concealed in it? As far as I know, many checks of this type share the EXACT same pattern on the back. Different patterns can be seen on other checks and bills.
If it is steganography, are we able to decipher the message from the pattern? What possible methods or reverse-engineering technology could be used to detect the methods of concealment, provided that such steganography is not uniquely deployed in this case?