I have a photo of a couple of Coast Guardsmen from the early to mid 1980s conducting a practice intercept/search of a small boat. While one member frisked a cuffed suspect, his partner covered him and kept an eye on another cuffed and seated suspect with a 20" barrelled Remington 870 with a parkerized finish and standard (4+1) magazine and a bead sight.
I had initially thought it to be an Ithaca 37, since the two receivers look similar from the left side, but confirmed it to be a Remington by the characteristic magazine tube cap with sling swivel base in it's center, where the 37 has a lug attached to the underside of the barrel that is in front of its cap and is the base for the sling swivel base.