I'm not familiar with the specific meaning or context of "MUM-139". This could be:

1. A product code or model number

2. An internal reference number

3. A code used in a specific system or database

4. Part of a longer identifier

Without more context about where you encountered this code or what field it relates to, I can't provide much more information. If you have any additional details about the context or source of this code, I'd be happy to try and help further. Alternatively, if you're looking for information about a specific topic related to this code, please let me know and I'll do my best to assist you.