I just got back from Avignon over the weekend. We took the eurostar from London to Lille and then the TGV down to Avignon.
The police were out in force in Lille. The luggage lockers and luggage office were all blocked off or closed. The elevators to the platforms were also shut down.
The luggage holds at the end of the train cars were open on the Eurostar (London-Lille-Paris). However on the regular French trains use of the luggage holds was not permitted. All luggge had to be stored above the seats in VERY small areas. On some train car people had ripped off the security tape covering the luggage areas and stowed their bags. At each stop these passengers stood by thiers bagd until the train departed the station. Finally they were told to remove the bags from the area.
Obviouslt this made the compartments a bit crowded! I do not know how long these security measures will be in place- but PACK LIGHT!

we were recently on trains round trip out of austerlitz station and paris est. all trains had red tape blocking access to the luggage racks at the end of the cars. (i also must point out that this was before the discovery of the device on the tracks.) naively, the first time i saw it, i thought the rack had been deemed too weak to hold luggage. only when i was on the next train and saw the same, did i realize it was a security concern. we had plenty of room in the overheads, but we were travelling light.

Does any of this PREVENT a bomb or other device being placed in luggage and left to explode? If not, is this merely window dressing and inconvenience for the sake of making people feel "safer"?????

It is window dressing to make the police look as though they're doing something. For years, left luggage facilities at French stations have been resticted to a handful of stations with manual left luggage. The very same stations will all have cars parked outside. You can put a bigger bomb in a car than in a suitcase and, over the years, there have been far more car bombs than bombs in train luggage. Checking luggage is futile when terrorists are just as likely to be suicide bombers prepared to kill themselves. There is no easy solution to terrorism, and making a show of closing luggage racks on trains will not stop terrorists.

Pretty much window dressing, I'd say, unless they're inspecting everybody's luggage too.

Have you ever passed the "Lost luggage" area in CDG, with the multitude of suitcases just sitting out?! ...very reassuring security. (not!)

Yes, I fear that most of these "security" measures all over the world including here in the USA are window-dressing. A bomb couldn't be placed in an overhead luggage rack?

The other day I went to mail a small package at my local post office, the first time doing that in a long time, I more often go to UPS outlets. Anyway, the clerk wouldn't accept mailing my package unless I could show a picture ID. Who would seriously think these days that a terrorist wouldn't have a picture ID, possibly even from a flight school?
If I identify myself with an ID listing my name as Ima Terrorist, what have I reassured anyone about? If they all feel better after seeing any old ID, THAT's what worries me.

I have to agree that, unfortunately, this is just window dressing.

A person could just as easily put a suitcase on the overhead rack as in the luggage compartement and get off at the next station.