FACT: All sprays of players you encountered at one point in game is stored in your computer.

They don't need to spray the wall in order for you to get their spray, you just need to have played in a game with them before.

If you would like to browse and pick one of these sprays, follow these directions:

• A window will pop-up showing you the left 4 dead 2 files. (If it shows you elsewhere, you need to find where you l4d2 files are located. Usually in this directory: C:\Program Files\Steam\steamapps\username\left 4 dead 2\l4d2)
  
• From there, go to "materials", then "temp".
  
• There you can pick a spray you would like to use. The amount of sprays you see in there depends on how many players you have played with before.

If you would like to get a specific spray you've seen before, follow these directions again:

• By default, the files are sorted according to their names. If you sort the files according to their "Date Modified", you are most likely to find the spray you are looking for by remembering the day you've seen the spray for the first time.

Have fun with your new sprays!