You might guess that a memorial inscription abbreviation ILMO means "In loving Memory of", STTMO means "Sacred to the Memory of" and IELMO "In ever loving memory of". How about EIR or WOTA?
If you know them you don't need to go to the list at gravematters.org.uk
although there may be other material of interest if you're contemplating a cemetery transcription project. The site is written based on Oxfordshire and Berkshire experience.