To the Anons that were posting about ADS-B and planes without callsigns or not showing on radar sites, etc.
Look in Planefagging 101 for the posts about the planes with 2-Reg, M-Reg or ZJ-reg (Guernsey, Isle of Man or Jersey). These planes are allowed 'Military' rating for some reason, even though they are civilian planes and that allows them to bypass customs and immigration checks.
I'll leave you to think about that for a moment and what possible activites could be carried out by these planes without oversight The aircraft registries are posted in Planefagging 101 in the Catalog..