The CCA manual tells the back judge to raise his hand at 10 seconds, hold it out sideways at 5 seconds, and slowly lower it until it reaches his body as time expires. Why re-invent the wheel, when a solution already exists?
Why?
Simple answer is;
CCA stands for
Collegiate Commissioners Association! Additionally, this is a extremely rare mechanic since NCAA Fields are required to have visible play clocks.
On the other hand, the NFHS has a publication entitled
Football Game Officials Manual which recommends the B in 5-Man
(R in 4-Man) will give a visible signal with 5-Seconds remaining.
While everybody has an opinion, a reasonable may assert, deviating from the NFHS Officials Manual could be considered
re-inventing the wheel when working NFHS contests.
My 2 cents
FYI - In OREGON, the B simply raises his/her hand (and nothing else) with 5 seconds remaining on the invisible play clock.
This will remain the mechanic for 2019 signal regardless of a 40 or a 25 play clock.