It seems like nearly everyone has done a version of the Pigpen Cipher. This one is done according to actual source material, and it's 5x5 so it's extremely small.
This is a randomised Pigpen Cipher (Also known as a Masonic cipher, Freemason's cipher, Napoleon cipher, and tic-tac-toe cipher)
Randomised to provide an extra layer of difficulty, and includes a variant on the grid symbolism to allow for some punctuation, numbers and basic maths.
(Designed this with DnD campaigns in mind)