The 18-year-old model flashed her million-dollar smile Wednesday at the Women's Guild Cedars-Sinai Annual Luncheon at the Beverly Wilshire Hotel. She was also flossing some new jewelry around her neck.

You'd be hard-pressed to say the "P" necklace has nothing to do with Pete ... unless you wanted to ignore the fact they've been on 2 dates -- that we've seen -- on 2 coasts in recent weeks.

As we first reported ... Kaia and Pete were spotted having dinner a couple of weeks ago at Sadelle's in NYC. If you look closely, she's wearing one necklace during that date. It's the same one she was wearing -- next to the "P" necklace -- at the Bev Hills event.

So, let's cover all bases here -- Kaia's brother is Presley, but wearing a "P" to honor her bro would be kinda weird. Kaia's middle name is Jordan, so that ain't it. Her mom Cindy Crawford's middle name is Ann, so no dice there. And, pops Rande doesn't have a middle name.