I would bet a hundred burgers that the plane has tail numbers.
They are likely small but legal.
Please remember that things that are not made "illegal" by laws or regulations (don't get me started on those) are in fact "legal".
Sometimes things that are unfamiliar to us appear to be odd, unusual or even illegal.
These things might be quite routine in the circles in which another person might travel.
For example, have you ever seen a banner towing aircraft pick up a banner?
It looks like a Kamikaze attack!
