no client needed for X signs
if you want 4 bits for buildable health that client will see
(it was 5 before but timbo rised it to 12 since it was not sufficient
so 4 is not near being good)
to use 12 bits you need new client
marking is server side even if client dont see the mark X
he will be marking anyway
edit.
you need 4 bits for mark,spawn,dcc,power
and 4 bits left for health since generic1 is 8 bits
I wonder what dcc bit is used for :/