If you are are planning to ride here in France all the fixed speed cameras I have seen have a warning sign followed by a sign telling you the speed limit (usually 70, 90, 110 or 130kph) and finally followed by the speed trap/camera itself. This may be forward facing, which means all they'll get is your smiling face or rearward facing which means they'll get ayour UK number but luckily no summons will follow you home. The concern is that if you're using a satnav with these camera warnings you may get fined. However how this will be implemented is unclear. Are the French police going to be trained in how to check the vast number of devices to see if cameras warnings are present and/or enabled? I think not.
I've been riding in France for 12 years and living here for about 18 months and only been stopped once at a road block where everyone was being breathalysed. They are getting increasingly hot on drink driving here and I'd strongly recommend staying off the wine and beer when riding. Random speed traps are also common and can be set up anywhere in towns, villages, back and main roads and of course motorways. The only warning you are likely to get is other drivers coming the other way flashing you with their headlights. They can issue on the spot fines and may accompany you to a cash machine or bank for payment or if you are seriously over the limit they can instantly suspend your licence and impound your bike.
In my view you are much more likely to get caught speeding with a randon trap or fail a drink test from too much drink at lunchtime than getting busted for using an illegal satnav and the first two can easily be avoided by good observation and some common sense.