This works for any client on a multi-player game. Enable the gl_nobind 1 code to make all the textures look like a series of numbers and letters, then spray paint or have someone else spray paint. By luck or chance, the map will be a flat unlit color of the spray paint and all the textures of the sprites will be the image of the spray logo. All players will be a brighter shade of the color, making them very easy to locate. Note: All the fonts will be corrupted, making typing messages or console commands difficult. To solve this, restart the game. Since navigating around the flat-colored level with this vision is hard, you might want to bind an alias to a key to turn it on or off. In the following example, holding down the key toggles it on; releasing the key toggles it off.
alias +see "gl_nobind 1" alias -see "gl_nobind 0" bind +see