[There's a mental question mark as Shepard raises an eyebrow. Why would it be anything but?]

Accidentally. Didn't even realise I was still carrying it until I saw I had both of them — my mistake entirely.

[She sorts in her other pocket with the free hand, balancing the datapad still under one arm, and pulls out, via completely normal methods, the other coin.]

Turns out, they're actually two halves of a whole. Watch--

[Bringing the two coins together, they attract like little magnets, and click into each other — making a single coin, plus on one side, minus on the other.]

--Only figured it out because I had them both in the same pocket. [Giving the two coins a light twist, they pop apart. This time, she holds them both out.]

You can have them both, if you like.