Laurel is the symbol of Blanche's past and all the bad things that have happened there and the innocence of Blanche was taken there.
Laurel can also be symbolized as the destruction of Blanche because Allan killing himself there is what starts her downfall in the first place. And at the end of the play is what comes back and destroys her relationship with Mitch in which decimates all hope she has of a future in New Orleans.
"he met you in Laurel, but I figure he must have got . you mixed up with some other party because this other party is someone he met at a hotel called the Flamingo"
"The trouble with Dame Blanche was that she couldn't put on her act any more in Laurell"
Streetcar Named ...
"They told me to take a street-car named Desire, and then transfer to one called Cemeteries and ride six blocks and get off at- Elysian Fields!
This line by Blanches gives symbolism of her whole life and journey in New Orleans.