Thanks, Frances
I should have known that you and the wonderful Manx Notebook could answer some of this for me.
I quote:
The punning motto 'Quocunque Jesseris Stabit' -generally given as 'which everway I am thrown I will stand'. However the verb 'jeceris' is the second person ('thee') of the future perfect tense of iacere, to throw, hurl, and thus the phrase is probably nearer 'whateverway you will have thrown [it] it will stand'. The motto first made its appearance on John Murrey's silver penny of 1668 where it could be read as 'however it is tested it will pass' which is not a bad motto for a coin for those times when false coins abounded. Possibly these coins gave its familiar association with the three legs