I broke mines 2 years ago. I didnt realise it was broken until a month after the accident. I was then in a arm cast for 6 weeks. I took it easy for another month, then was back on the bike. Now I hardly ever notice it day to day, unless I try breaking a fall using my hands (natures warning reminder).
Tell-tale signs are tenderness in the "snuff box area" of your thumb/hand. Pressing hard into it causes pain. Prior to cast, I would also occasionally lose grip when trying to lift something heavy single handed.