LILO $22K LUV RING thumbnail

Nothing says "serious" like being gifted with a $22,000 diamond ring from Cartier’s — and that’s just what Sam Ronson gave gal pal Lindsay Lohan.

One minute the two lil’ best buds were out shopping in El Lay running the pap gauntlet, the next LiLo was sporting some beaucoup bling.

Reportedly, Ronson, 30, bought the sparkler for Mean Girls star Lohan’s B-day. 

Lindsay turned 22 – hence the $22,000 ring-a-ding-ding according to the UK’s The Mirror

And you know lez luv is in the air when Ronson’s also posted the infamous kiss pic with Linds on her MySpace page.

It’s in Sam’s photo gallery – not her profile pic – for those of you keeping track of such ephemera.

Speculation is rife with blog-aholics that with LiLo in LA, a same sex marriage may be the offing with platter dropper Ronson, but no invites have been e-blasted as of yet.

Presumably, the key to keeping a "secret, under-the-radar affair" is being outted-in-the open about it.