Common sense, good manners and dignity should be used when flying the Union Flag, a foremost expert has argued.
The comments came after a hybrid with the Israeli colours was run up a lamp post on a main road in south Belfast.
The flag, approximately half the UK's flag and half the partial hexagram and Star of David, was flying on Milltown Road, close to the junction with the A55 dual carriageway.
Israeli and Palestinian flags have been raised in various parts of Northern Ireland following the October 7 Hamas attack on Israel, which was followed by weeks of Israeli bombardment and then invasion of Gaza.
Malcolm Farrow, president of the Kingston-Upon-Hull-headquartered Flag Institute, said he was not impressed by the combination.
"I have to confess I don't like it much. It simply divides a community once again. Not what flags are supposed to be for," said Mr Farrow.
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Founded in 1971, the institute is a members' association "devoted to the study and promotion of flags and vexillology....an independent organisation – international, inclusive and informed".
Mr Farrow noted he has seen a hybrid of the Union flag and the Ukraine flag, including one flying close to where he lives. He added the laws in flag flying are much stricter in the north compared to Britain.
"On the UK/Ukraine flag, you can see the point and cannot imagine many people objecting. With the Israeli flag, it is similar, but it is a lot, lot more divisive," Mr Farrow said, adding that there would be nothing to stop someone putting up a hybrid with the Palestinian colours in the next street.
"It is not really good for community relations, not really a good idea," he added.
"If I could sum up it is all about common sense and good manners and dignity."