What does the stamp A51 on a ring mean?

This was first introduced in 1798 and can now been seen on all UK hallmarked gold that's 9, 14 18 and 22ct. The crown also appears on old 12 and 15 carat gold, however this was stopped in 1932.

Gold electroplated

high grade silver product

i think it mean( love u 4 evr )or some thing like that but im not sure>>> sory.