Everything that is on a flag
A star, a crescent, a lion, a ship. 36 of them, across 171 of the 254 flags — and every entry quotes the sentence that put it there.
star
75 flags
coat of arms
30 flags
cross
22 flags
crescent
18 flags
sun
18 flags
bird
17 flags
writing
14 flags
leaf
11 flags
shield
11 flags
eagle
8 flags
tree
7 flags
crown
6 flags
saltire
6 flags
wreath
6 flags
flower
5 flags
sword
5 flags
globe or map
4 flags
building
3 flags
fish
3 flags
lion
3 flags
moon
3 flags
mountain
3 flags
human figure
3 flags
ship
3 flags
spear
3 flags
other animal
2 flags
book
2 flags
dragon
2 flags
key
2 flags
other weapon
2 flags
chain
1 flag
grain
1 flag
hand
1 flag
torch
1 flag
trident
1 flag
wheel
1 flag
What these numbers are, and are not
They are counts of flags whose own article says the thing is there. They are not counts of flags that have it. Every tag was proposed by reading each flag's English Wikipedia article, and then read again one at a time — about half of what was proposed was thrown away, because a sentence mentioning a star is often about the flag a country flew until 1962, or about the neighbour's.
Where an article never describes what is on the cloth, its flag is on none of these lists.83 of the 254 are in that position. That is a gap in what has been written down, not a claim that those flags are plain.