Do you mean "Ambigram" ; a typographical design or art form that may be read as one or more words not only in its form as presented, but also from another viewpoint, direction, or orientation.
SIS
Paul was not crucified upside down, he was beheaded. Peter was the apostle that was, as he said he did not deserve the same death as Jesus.
A circle or a square.
this \
Is a number that reads the same whether you read the digits from left to right or from right to left.
Something that looks the same upside down has point symmetry.
1961
NOON
NOON
MOW
Some types of ambigrams read the same from different perspectives.
The word is NOON.
NOON
This is an ambigram.
SWIMS
The word SWIMS, when written in upper case letters, is the longest word in the English language that reads the same both forward and upside-down with no reading difficulty.
No. It's unusual because it reads the same way upside down, but it's not odd.