Sinclair and other officers are pure EA military, so they get the
EA pins on the chest. (Also the techs wear them in the dome, and others
in charge of various divisions.) Security is under the jurisdiction of
EA, but are a separate component, staffed under B5 financing. These, and
medical, and scientific and environmental and other areas have their own
symbol, which is worn on their chest and shoulder. You can tell who works
for EA because they have the EA also on their shoulder, whereas those who
are employed directly by B5 have the B5 symbol on their shoulder.
The patches connote specialization: command is a starburst, lines that
radiate into every area; security is a gunsight/targeting symbol; medical
is a stylized medicine symbol, and so on.
Sinclair and Ivanova wear their officer's bars on their epaulets; not
the triangular part per se, but the bars at the very far end of the
epaulet, below the triangles.