Anyone Identify AM5SS beacon?

This morning something started to intermittently break squelch on 146.52 and, after a few minutes of it getting stronger and more irritating, I realized it was beaconing in code: MO MO MO MO MO DE AM5SS
This went on continually for about 10 or 15 minutes, with the signal gradually fading away. It sounded like modulated FM or AM, not exactly on the frequency of 146.52 (although that was the clearest I could make it out after tuning up and down). AM5SS does not show up as a beacon or whatever in my online searches such as Google and QRZ. Hoping someone knows what the heck it is. I guess I should go outside and look up in the sky to see if there's a balloon of some kind.... but now the signal is gone, thank goodness.
Jim W5AOX