There is no indicator, no. If you have a special app or software you can log the engagement of the rear axle but otherwise there is nothing to tip you off during normal driving, and no way to force 2WD (again, unless you have special software like AlfaOBD).
Jeep wanted to make it 100% automatic and require nothing from the driver, any idiot can just get in and go and if the situation calls for AWD it will do it, when it can it will disconnect the rear axle to save gas. Pressing the 4x4 button just prevents it from ever going back to 2WD until you turn that off. Its hardly necessary, mostly that button exists as a gimmick for those who come from true 4x4 trucks and to try to differentiate themselves from say an AWD Kia, but its still just a glorified AWD car with automatic part-time 2WD capabilities.