First off, I'm American, so my English isn't very well either.
Yes, this has been discussed a whole lot on this website through the years and years and years. What is that thing?
I just checked out an Auto Enthusiast website where this same question about Columbo's car "dashboard wire thingy" has come up. The consensus there is that the wire is an "after-market add-on" in France. It is said to indeed be used to stuff items into so as to keep them in place. Apparently these were common place on French Taxis in the 1950s and 1960s according to that website. It's where they could shove maps and newspapers and stuff.
I just spent a couple hours looking at images online of French Taxi cabs from the 50's and 60's and I couldn't spot this wire add-on on any of them.
In fact, of all the images I looked at - outside looking in and inside looking straight at the windshield - of Peugeot 403 autos, only two of those hundreds of photos showed that same wire.
An identical "up and down squared" wire appeared on the dash of another 403 cabriolet. The other was on a 4-door sedan, but that wire was not "up and down". It was full across, looking like a miniature ladder (with steps) going across the entire dash by the windshield.
And then there's this...
There were LOADS of photos from Columbo of the car. There are many of these photos that show NO wire across the dash. For instance, there's a close-up from "Murder of a Rock Star". It's of the police-lady wearing the Columbo-mask, while sitting behind the steering wheel of the car. You get a great view of the outside looking in of the windshield/dashboard. The wire-thingy is NOT there.
Perhaps this wire-thingy could be put in a "down" position? Then too, there were a couple of different Peugeot 403 Cabriolets used in the series. Maybe one of the cars had the wire-thingy and the other didn't?
Loads of the photos of other 403s taken on the inside of the car looking at the dash CLEARLY show that there is no wire atop the dash.