US officer insignia is pretty nuts - same shape but different colour for O-1/O-2 and O-4/O-5; and random shapes for O-4/O-5 and O-6; plus different number of items for some but not all.
US originally was board with 0/1/2 bars for O1/O2/O3
Board with fringe and 0/1 oak leaves leaves for O4/O5
Board with fringe and Imperial Eagle for O6
Board with fringe, imperial eagle, and star for O7
When they did away with the fringes, they also made O4/O5 oak leaves, but increased the numbers to 1 & 2, and did away with the eagle on the board for O7's, and added a second star for the O8's, and a third for the one O9.
Note: they had silver on gold or gold on silver, by branch. They kept the army infantry's silver on gold, then went to silver on branch color, then, when they did away with the 1x4" boards on the shoulder, used the old gold bar and leaf for O1 and O4, since the bar no longer made it clear.
US Naval cuff stripes were 1 for midshipsman, and 1 additional per grade O1+... then, in the 1890's, since normally, they were worn with a stripe width and 3 stripe widths separation to form groups of 2 stripes...
Eg: O4
|| | || and O5
|| || || ... but O6's often wore them as
||| | ||| and the O7 as
||||||||...
Then they later turned pairs into a wider stripe, and gave O6's 4 wide ones rather than the 3 wide and 1 narrow, as other Navies were using 4 wide for a captain as well... And the admirals had 8-narrow-stripe-wide extra-wide stripes.
It's all sensible IF you know the history.
@Hans
Positional variance by grade has been used in the past.
For a while, the UK Navy differentiated the ship's first lieutenant by moving his one shoulder board from one side to the other. Commanders got a fringed board, captains two fringed. Masters Commandant got the board on the other side, like a ship's first lieutenant.
The US navy originally differentiated CPO's from Midshipsmen by where they wore their Eagle & fouled anchor... Midshipsmen on the lower arm, CPO's on the upper. Petty Officers wore an Eagle and non-Fouled anchor... which side told which specialty for PO's and CPO's... Midshipsmen wore it on side by whether they'd passed yet or not.
Likewise... US Army Technical Grades... Originally, they got inverted stripes. Then, they went to matching stripes with a "T" between the arms of the chevron. Then back to inverted stripes, with a T between the arms of the chevron. Then the inverted PFC chevron and rocker got an eagle for E4, and rockers above for additional grades...
Likewise, "positional trainee grades" (Acting Sgt/Plt Ldr, Acting Corporal/Squad Leader) were worn pendant from the right breast pocket or on a black brassard (strip worn on left arm), while real NCO's wore the exact same insignia as either sleeve stripes (dress jackets) or collar pins (undress uniforms), or subdued pins or patches (field uniforms). This one was in Ft Dix in 1987. (I hated having those damned gold chevrons on my BDU's... had to wash them nightly.)