Jennifer Lopez is celebrating her birthday week out in the Hamptons without Ben Affleck around whatsoever -- but there's still a remnant of their marriage in the picture.

The triple-threat entertainer has been out on the East Coast for a little while now, and it looks like she might be sticking around there through her 55th birthday -- which falls on a Wednesday this week -- on account of the fact she was out and about there Monday.

J Lo was photographed cruising around town in a cozy cardigan with a midriff top underneath -- all color-coordinated of course -- but notably ... her wedding ring was on her finger.

The reason that stands out ... she and Ben have, at times over the past few months, had a bit of disappearing/reappearing act going on with their marriage hardware ... and that applied to a weekend social media post Jen threw up where her wedding ring was gone.

The other thing that's noticeable about Jen's extended Hamptons getaway ... Ben hasn't been there at all. He's here on the West Coast, and he too has been ditching his wedding band here and there ... including on Saturday when it was nowhere to be seen while he was out.

As we've reported ... Jen and Ben's marriage is on the rocks -- he's moved out of their marital home, and now they're trying to sell that place ... and haven't shown PDA of late.

Considering Ben may very well miss Jen hitting the big 5-5 ... it ain't a good sign.