Forget the engagement ring -- Zendaya's "T" tattoo also had Golden Globes viewers buzzing ... and TMZ can confirm it’s part of her matching ink with her new fiancé, Tom Holland.

Sources tell TMZ the couple hit up Boston Tattoo Company in Massachusetts the day before Thanksgiving with a clear plan: something small and discreet, staying hidden -- with Tom getting his matching "Z" on his ribcage, mirroring Zendaya's.

It was a family affair -- we're told Zendaya's mom tagged along and got a small tattoo too. As for the lovebirds' pain management? They handled it like pros!

While the shop's minimum is usually $150, the artist gave them a sweet discount, bringing the price down to $100.

The couple even snapped pics with the staff, who we're told were totally starstruck and had jelly legs, 'cause it was the first time big names like them walked through the door. The tattoo artists couldn't help but gush over the pair, saying they totally felt the love between the newly engaged couple.

Fans noticed Zendaya's tattoo at the Golden Globes -- the same night she was wearing her new engagement ring for the first time at a public event. TMZ confirmed the news the next day ... Tom popped the question over the holidays, in an intimate setting with just the two of them.

Looks like this is permanent -- congrats!!!