Two possibilities:

Given the vintage (2017), “rm” more likely indicates RealMedia or a release group tag.

Check if hmn604 matches a known database:

If no results appear, treat the file as potentially dangerous.

This string is a classic example of an auto-generated or database-tagged filename. Here is what the components typically represent in this context:

Use Google with quotes or a metadata analysis tool like mediainfo. Do not visit any suspicious URLs embedded in the string (e.g., “hdtoday”).