Dick was observant. In his line of work, he had to be. When investigating a potential crime scene, every little detail could lead to much more.

A bigger picture, one he wouldn't have found if he wasn't as observant.

Not to mention that he was trained by the greatest detective in the world, the one and only Bruce Wayne. You know, aka Batman. Gotham's local vigilante?

So imagine his surprise when he sees his younger sibling walk in, wearing some loose clothing, and the eldest sees a certain body modification on them that wasn't there before. He had checked if it was fake, like one of those things one could put on your skin with warm water and would stick for a day or two. Nope. It's real. Very real. How did this happen? When did this happen? Did anyone else know about it?

Sure, you were old enough to decide for themselves, but being kept out of the loop sucks. Like, majorly. He wants to know what goes on in his siblings lives, sue him.

"Hey, uh. When did you get that?"