When Cortez - under the name "Manny Chavez" - parted ways with Brian Westhouse, he gave him an old pocket watch and told him: 'When my heart starts beating again, I'll know.' The pocket watch wasn't ticking and Brian didn't know what to make of it, but he kept it. When April first came to Arcadia, Brian gave her the watch and, using a pushpin as a winding mechanism, she managed to get it ticking again. This seemed to be some sort of signal to Cortez, as he then apparently triggered a Shift that allowed April to return.
There is clearly a connection between Cortez and the watch, but it's never fully explained. The watch stops ticking when Cortez and Jacob McAllen fall from the MTI Building; April exclaims that it must mean Cortez's heart has stopped beating, but the watch hadn't ticked in the time Brian Westhouse had owned it. It's possible April still owns the watch.
Obtained from Brian Westhouse.