Green’s Dictionary of Slang

sheckles! excl.

[? euph. for shit! excl.]

a general excl.

[UK]E. Pugh Spoilers 164: ‘Sheckles!’ said he contemptuously.
[UK]E. Pugh Cockney At Home 197: ‘But it ought to be everywhere,’ I broke in. ‘Sheckles!’.