Under Serout2 they give explanations of the {I} and {S}. My manual has it on page 143. {I} will send an indication character "%" for binary, "#" for decimal and "$" for hex values. {I} will send negative numbers if bit 7 is a one. Google "2s complement" if you don't know how negative values are computed.

Consider:
B0 = 16
Serout [SBIN B0] would send %00010000
Serout [SDEC B0] would send #16
Serout [SHEX B0] would send $10

B0 = 255
Serout[IDEC B0] would send -1