These are the screen used prop license plates that were on the character Loomis' 1968 Chevrolet Caprice station wagon in the 3rd season episode "Carpenter Street". They are made of vacuformed plastic. The artificial aging on the front plate is an exact match to that present in the same plate as seen in the screencap in photo 4. (Compare the plate number '4')
From Memory-Alpha.Org, the Star Trek wiki: In 2004, a group of Xindi-Reptilians from the year 2153 made their hideout in an abandoned warehouse located on this street, where they began to synthesize a bioweapon to use against Humankind in the future. They employed the service of Loomis to abduct eight individuals of different blood types and bring them to the warehouse, where the Reptilians would extract blood samples and use them in producing the viral toxin to be used for the bioweapon. Loomis had brought six victims to the Carpenter Street warehouse before Jonathan Archer and T'Pol intervened.
Archer and T'Pol, who had been brought from the future by Daniels, forced Loomis to get Archer into the warehouse, with the Starfleet captain pretending to be the seventh victim. Fooled by the deception, the Reptilians were killed by Archer, although the lead Reptilian, Damron was nearly successful in releasing what there was of the viral agent. With the plot to create a bioweapon against humanity foiled, Archer and T'Pol were returned to their own time along with the dead Xindi and their technology.
The following morning, members of the Detroit police department arrived on Carpenter Street to place a bewildered Loomis under arrest for the abduction of six people.