There are 4 locations for a file named 'xj_v_ph_signs04' in the Metropolitan Emergency Station Pack. There are 2 textures that look like the above pic. One is located in 'hei_heist_dlc_police_txd+hi.ytd' & the other in 'hei_heist_dlc_police_txd.ytd' both in the same location here:
It's also the same case for this texture below, again of the same name ('xj_v_ph_signs04') even though it is a different texture (yeah, I don't know who Fozzy is so I'm covering all the bases):
There's one in 'v_47_sheriff_txd+hi.ytd' & one in 'v_47_sheriff_txd.ytd' both located here:
Depending on your graphics settings the game will choose either one of the textures versions in '+hi.ytd' or '.ytd'. Replace both versions of the texture you want to change just to be sure.
Note: There are also versions of the same files elsewhere in the game. Here for example:
The textures there look like this:
Just make sure they aren't the ones the game is using
I that doesn't solve it I'd look at embedded textures hidden away in one of the .ydr etc files.