The Imperial Security Bureau is an intelligence and security organisation which also takes overt action to encourage the populace and military personnel to remain obedient to Imperial policy and ideals. It is an important branch of the political organisation known as COMPNOR - Commission for the Preservation of the New Order. As such it is ultimately answerable to several of the Emperor's court advisors, especially COMPNOR patron Crueya Vandron [The Imperial Sourcebook]. (The rival Imperial Intelligence organisation reports directly to the Moffs, Grand Moffs and the Emperor himself.)
Several ISB officers were seen aboard the Death Star in A New Hope. There they were charged with maintaining the morale, assisting in security matters and providing Death Star commanders with intelligence information from the ISB organisation throughout the Empire.
The first ISB official seen was Colonel Wullf Yularen, who sat beside the vocal Admiral Motti in the main command conference room. Yularen's age and rank make it probable that he was the most senior ISB officer aboard the battle station. The only open question is whether there might have been an ISB "General" or equivalent also on the Death Star. At least one other ISB officer sat at the conference table, and it seems probable that this other officer was either Yularen's immediate superior or his second in command.
Several other ISB officers of lower rank were seen walking the Death Star's corridors. They seemed especially numerous in the region around the repulsorlift tubes cluster which led a small band of disguised rebels to Princess Leia Organa's detention block. Presumably there were several security-related facilities in that vicinity.
Our knowledge of the rank system of the ISB is very limited. Only a few officers have featured or been named in work published to date. All of these seem to have been members of the Surveillance division of the ISB; concerned with the observation of regular military activites. We therefore do not know whether ranks are used throughout the entire ISB. It is possible that Surveillance staffs' ranks are merely formal, for the purpose of determining seniority relative to the regular military personnel with whom they work. An ISB Colonel working with the Army would be addressed as a naval Captain if he changed to work with the Navy.
In any case, the known ISB ranks are a curious mix of Army and Navy traditional ranks. They are as follows:
Colonel Yularen provides us with an example of the uniform of a senior ISB officer. Like senior officers of the regular military, Yularen declined to wear a cap. (But of course, it may just be that it's bad manners for a seated man to wear a hat.) All presently-available images of him show him sitting to the left of Admiral Motti at a conference table aboard the first Death Star.
Images: [Yularen's SWCCG card] [Left side view; no cylinders] [ Conference Room, left of Admiral Motti] [ Again with Motti]
Two ISB officers passed Solo, Skywalker and Chewbacca in the Death Star corridors on their way to recue Princess Leia Organa. These men had badges which seem equivalent to either Colonel, Captain or Commander, although they had no rank code cylinders. The ranks of Commander or Colonel are preferable, because we know with certaintiy that these rank exists within the ISB. (In addition to Colonel Yularen in Grand Moff Tarkin's conference room, a particular ISB Commander Mar Barezz appears or is mentioned in at least two Roleplaying Game references.)
Another ISB officer spoke briefly with Grand Moff Tarkin in the main Death Star control room shortly before the station reached the designated firing position. Unfortunately this officer was too far from camera for his insignia to be read, but he seemed to lack rank cylinders. He was dismissed by Tarkin immediately before Lord Vader brought Princess Leia to observe the superlaser demonstration.
[To left of Tarkin.]
It is probable that ISB insignia does not always require security code cylinders in the same way as military personnel. The general nature of their duties makes this plausible. Roving morale and security officers would not require special access to particularly special military areas or data terminals.
Images: [Clear view of both insignia.] [ Both approaching camera.] [ Both in closeup.] [ ISB officer 1]
[For further information, refer to the ISB subsection of Summary of Uniforms.]