Check out what Hiberno-English.com has to say:
segocia, skeowsha, segotia: n. colloq. old friend; term of endearment (origin obscure; it has been suggested that it derives from a corruption of Ir. ‘seo dhuitse!’ (= here it is you are!);
James Joyce, Finnegans Wake (Part:1 Episode:7 Page:215). 12-13; “Ah, but she was the queer old skeowsha anyhow, Anna Livia, trinkettoes”
http://mv.lycaeum.org/Fin negan/viewpage.cgi?page=2 15&like=dea
(Please note that Finnegans Wake was published in 1939).
“Irishman’s Diary”, The Irish Times, 23 June 1965, p. 7: ‘’Segocias and Segotias. Where did John Molloy get the title for his new show, opening at the Gate on Monday next? Well, it’s a logical progression. Molloy’s last show was called ‘There Y’are’, and whenever a Dublinman says ‘There y’are,’ he inevitably follows it up with ‘Me oul’ Segotia.’ So ‘Me oul’ Segotia’ the show becomes.”
As for the derivation: “One story has it that members of a club called ‘The Oul’ Segotias’ never tipped less than half a sovereign and that when less well-heeled passengers tipped tuppence, the jarvey (q.v.) would say with that deleicate irony that typified the breed: ‘T’ank you, me oul’ segotia.’”; the same column on 1 October, 1965, p. 9, cites Donn S. Piatt as suggesting that “Segotia has been Gaelicised as ‘sagoiste’ and may be connected with French ‘sacoche’— wallet, money-bag, saddle-bag.’” , Roche, Tumbling Down, 28: “‘Hickey, me auld segotia,’ my father piped. ‘How are you keepin’ Paddy said as he slided through the crowd”.