Optio staff

[SOCL]

Cowen doesn't actually show a tesserarius, but mentions them carrying said staff:

In numerous funerary sculptures [the optio] is represented with a long staff tipped with a ball-end. We know from the late Roman military handbook written by the Emperor Maurice that officers were positioned behind the battle line during combat (Maurice, Strategikon, 12.b.17; Speidel 1992: 24-26). This was surely the function of the optio's staff. Tesserarii (officers to the watchword) are also represented with this type of staff and their function in battle should be considered similar to that of the optiones.

Unfortunately, Cowen gives no source to back his assertion.

Can anyone point in me in the correct direction of such artwork or funerary scultpures so I can get an idea of this? I've seen reconstructions of them, varying from a wooden ball-end (i.e. Matt's) to having a metal ball-end (i.e. Legio VI FFC's). I have also seen Legio XI's and it took has a metal ball at the tip, though it is more than a ball, attached to a metal fitting over the top of the staff.

Basically, I'm trying to figure out what sorts of materials to use and suggestions for construction.

I seem to also recall a butt-spike on the bottom of most. Would this be similar to the same as a butt-spike on a pilum? :?