Corpse, sm_removespray teleports the spray to 0 0 0. However, a few maps actually have this visible in your map, so if you wish to hide it completely, edit it to "0 0 -9000" or something of the nature.
And I'll repeat, sm_adminspray works fine, you simply can't spray on all the surfaces that you can as a normal spray. I went through and tore the code apart trying to resolve this issue and tried a few other methods, but none of them work as well as the current one, so you just have to deal with it.