The famous bracelets ...
As explained in my article about one day in the La Vache Qui Rit "caravane publicitaire", each invited person to the Tour de France has one or more bracelets which indicate which parts of the Tour he/she has access to.
The bracelets have the date, the Tour de France logo and the year printed on it, so they can only be used on one specific day. When you put them on you have to close them tight enough around your wrist so you cannot easily glide them off over your wrist and your hand; once you've put them on you can only remove them with a pair of scissors (and still this is difficult ...); this is of course done so you can not give the bracelet to someone else during the day.
On this picture you see the caravane publicitaire bracelet of July 20th on the left, than the bracelet for the Espace Tourmalet VIP part at the arrival for July 22nd in the middle and finally on the right the Village Départ bracelet also for July 22nd.