"Year over year refers to the mathematical process of comparing one year of data
to the previous year of data."
Source: https://investinganswers.com/dictionary/y/year-over-year
While we could sign the concept year-over-year using various combinations of
signs or fingerspelling -- I would suggest to you that more often than not
"context" allows us to sign the term year-over-year by simply signing
"every-YEAR"
Sample: https://youtu.be/ni0cj_Uva2I
To support that idea (of just using the "every-YEAR" sign) consider this example
of real life usage provided by Merriam-https://www.merriam-webster.com/dictionary/year-over-year
:
"The society argued in the Journal of Forestry last year that this simple
accounting is reasonable in the United States, where forest inventories have
increased year over year since the 1930s.
-- Peter Fairley, IEEE Spectrum, April 2012"
In the example above due to the context of the sentence the fastest and most
simple way to sign "year over year" would be to use the "every-YEAR / annually"
sign (which, due to context takes on the meaning of year over year).
Sure, if for some reason the specific English terminology "year over year" needs
to be understood (as in a student taking an English-based test later on in the
semester) then be more specific in your signing including signing YEAR fs-OVER
YEAR combined with expansion (such as signing YEAR COMPARE YEAR time-RANGE,
time-RANGE) and later in the conversation shortening the concept to fs-YOY.
Notes:
The same approach applies to "week over week." In context it will likely be fine
to just sign "every-WEEK." (The version that repeats the sign week. Some people
write that as: WEEK-WEEK, or WEEK+).
In strong context and repeated usage it may become more efficient to eventually
reduce the term to fingerspelling "WOW" -- however use a small bit of caution in
fingerspelling WOW (for "week over week") due to the potential for the audience
misunderstanding the spelling to mean the exclamation "Wow!" -- since WOW (the
exclamation) has a fingerspelled version. This shouldn't be an issue when
communicating with a skilled signer though because the exclamation WOW! is
strongly inflected with facial expressions and tends to be lexicalized with
added movement.
Notes: