I know this is really delayed, but this is the Omega forums and the OP was talking about the Omega Seamaster Worldtimer and for this watch the font color of the city name indicates which cities use daylight savings time, and which don't. So you just add an hour if the city name indicates daylight savings in the summer. You can tell the daylight savings color by looking at most american cities like Chicago, LA and NYC that all follow daylight savings, but not Honolulu, and the font colors vary based on the watch face, but note that London is red to remind you that it is also GMT.
Doesn't apply to the tissots and most of the other pictures posted in this thread, but I thought I would mention it, because it's relevant and no one else posted it and I got here through google.