IT have confirmed my belief, as also noted by ChasB46.
They do not signify any change in the security of Shipspotting.com, but changes and inconsistent approaches to standard warnings generated by browsers when encountering 'http' sites - note that Pieter is not getting the ongoing little sign (a padlock with a red line through it) that I get even though we are using the same browser; at the same time Dirk kindly sent me a couple of screen shots, which showed different forms of the message on consectutive days.
Just a quick check across the webpages I have opened in the last hour shows that amongst the http sites that show exactly the same "alert" are Equasis, SeatheShips, Clydeships, Crewlist.org, Danish Government Shipregister, RFA Historical Society. This is not to be complacent but just to give a context.
Meanhile IT have confirmed "A change to HTTPS is on our roadmap for ShipSpotting and it is expected to be implemented in around 2 months from now."
@Andrecas. The old IT set-up indeed said it was "on the job" but actually never did anything.