It occasionally appears in optical character recognition (OCR) errors from archived newspapers, such as the Weirton Daily Times , where it is a misreading of unrelated text or numbers.
If you provide the context, I can give you a more specific answer about what it means for your device or project. Weirton Daily Times Archives, Apr 23, 1959, p. 16 such as the Weirton Daily Times
In technical specifications like HL7 Terminology , "47mp4" is used as a code representing the MP4 Video media type. such as the Weirton Daily Times