Anyone know what this is for?

[MS Coast]

Good info here. Adding an authoritative source:

NOTAM 00852

UAS NOTAM FDC 0/0852

udds-faa.opendata.arcgis.com

Getting there was a bit weird. It's listed under Documents after clicking on the search box.

It is accompanied by FDC 1/5318 for the navigable waters of the United States.

Thanks. I should have included the URL.