If you put your mouse over it, the hand will be RED. This indicates this will offend the NPC.
This is not actually true. I actually thought this was the case myself, but it's not. There are two colors: white and orange (in the case of crates it's a little more red as one side of the box icon is shaded darker). Mousing over nearly every (but not all) items will show an orange tool-tip, including crates. Once you open them, the icon turns white.
I would love to show you a screenshot as an example, but for whatever reason both Steam and Fraps remove the little "hand" or "box" cursor-icon when a screenshot is taken.
You can, however, go test it yourself or take my word for it: In the first town in the Legion warehouse is a guard (Sergeant Curtius) guarding a door. Next to him is a table with an apple and a piece of parchment. Both show an orange hand when you mouse over them - there is no difference between the two cues. If you take the apple, nobody cares. If you take the parchment, the Legion guards attack you for attempting to steal.
Edit: One moment, I got the cursor to remain in a fraps video. I'll take frames from that and posts the screenshots in a few minutes.
Edit 2: Here we go. I've overlapped the two pictures so the icons are as close as possible. Again, if you take the apple nobody cares. If you take the parchment, the guards attack you for stealing. There are no differences in color between the two icons.