RE: Civvie spotting question…

I’ve heard a few stories of people being told to leave certain airport when they’ve been there early in the morning or late at night.It is an unusual time for plane spotting!People acting strange around the airports is another occasion when they have been questioned by police.
I guess at an airport like FRA where you have both military and civil there is hightened security but I wouldn’t they are anti-spotter at all.