Where are you going?
I thought the 'sign of being a couple' was the asking of the question "where are you going?" so it stands to reason that the use of this app is a sign of imminent divorce - the level of mistrust that Alice* is showing by using this app would certainly seem to indicate this. It's one thing to ask, but something else entirely to check the answer.
* A process of logical deduction that it must be Alice that is using the app as her name is not shown in the picture, which clearly shows Bob as being a contact, so it's definitely not his phone we're looking at.