Eric Partridge gives the following in his A Dictionary of Slang
and Unconvential English (Supplement): pig's ear occurs in D. W.
Barrett, Navvies, 1880.—2A 'side light colour signal' (Railway,
3rd): railwaymen's: C. 20.—3. A blunder: mostly middle-class:
since ca. 1945. Elizabeth Hargreaves, A Handful of Silver,
1954l. '"I've made a real pig's ear of it, haven't I?" said
Basil, with an attempt at lightness.' (Laurie Atkinson, who
asks, 'Rhyming s. for smear?') In the main edition, "pig's ear"
is given as rhyming slang for beer. Richard A. Spears, in his
book Slang and Euphemism gives: Pig's ear! 1. an exclamation, a
euphemism for *Pig's ass! (q.v.) 2. beer; a glass of beer.
Rhyming slang. And since he mentioned the source of the
euphemism: Pig's ass (also Pig's arse!) an exclamation. For
synonyms see 'Zounds! [widespread slang, 1900s] which caused me
to look at Partridge's definition of "Pig's arse": Pig's arse A
low c.p. of dissent or disbelief: Australian: since ca. 1945. An
adaption of pig's eye — which, b