Miley Cyrus, Liam Hemsworth -- Married?

Miley Cyrus posted a pic on Instagram which shows her and Liam Hemsworth posing for an XMAS photo ... and Dax noticed something interesting ...

Check out Liam's left ring finger -- it looks suspiciously like a wedding band. The pose blocks Miley's finger.

They got engaged earlier this year but made no announcement about a wedding date.

And as long as we're talking, also take a look at another pic Miley posted, showing her in a Santa's getup. It looks like she might have 2 bands on her ring finger, one being her engagement ring.