The old imperial standards are well known to all of us. Do any of us bother to come up with flags of individual worlds? If you have, are there any conventions you follow?
I've to tough very long about it, and I've only designed a couple of flags to now (not enoug to make many rules of it)... However here are two rules I used:
1) Imperial systems flages show sunburst(s)
2) The number of sunburst(s) shown depends on the number of stars the system has
I use Sunbursts for Imperial, Corona Motif for Sector Flags, Starburst Motifs for Subsector Flags, and Stars for System-Level Flags. Usually mixing this with Hearaldry stuff can get pretty cool.
Imperial starburst: The starburst appears directly on the flag similar to the British colonial system. Settled in the year 87 Darcia’s flag reflects this
Starburst Influenced: Some kind of star is involved in the design normally in gold or red.
Settled during the late first Imperium Shirnkung’s flag of the year 8 reflects an imperial influence.
Independent: For some reason the world chooses to use no imperial symbols in their native flag.
The Virtuous Republic of Doasum is a loyal Imperial world but is a strict theocratic state. Their flag uses the symbols of their religion.