Rego collecting is something I can't quite understand but watching aircraft fly/land/whatever is fine
The spotters at Luton probably don't realise how they frighten the FA's who have to walk to their cars. The FA's don't know that they are "harmless" spotters and just see a "different" looking guy loitering around where the public don't usually go. This naturally unerves them a bit. They either get security or one of the male crew to walk them to their cars. Paranoid? No, I don't think so. The threat perception of a female is very different to a male's.