Green’s Dictionary of Slang

rubber heel n.

[note police jargon rubber heels, Special Branch, the internal investigations department of Scotland Yard, policing the police]

1. (US, also rubberglue, soft heel) a private detective; a store detective; a railway detective.

[[US]Van Loan ‘For Revenue Only’ in Lucky Seventh (2004) 216: A large, calm, horse-faced man in a gray uniform came in on rubber heels.].
[US] ‘Jargon of the Und.’ in DN V 463: soft heel, A railway detective.
[[UK]Leamington Spa Courier 19 Oct. 10/6: Edward Wynn is a rubber-heeled detective].
[US]G. Milburn ‘Me and My Bindle’ in Hobo’s Hornbook 262: When standing there before me was the Podunk rubberglue.
[US]Irwin Amer. Tramp and Und. Sl. 176: Soft Heel. – A detective; one who wears rubber or ‘soft’ heels.
[US]Monteleone Criminal Sl. (rev. edn).
[US]Goldin et al. DAUL 201/2: Soft-heel. (Hobo) A railroad detective.
[UK]J. Morton Lowspeak.

2. (also rubber-heeler) someone who spies on their fellow employees; thus rubber heel boy, rubber heel inquiry, rubber-heel mob.

[US]Berrey & Van den Bark Amer. Thes. Sl.
[UK]M. Pugh Chancer 91: You fancy yourself as a ‘rubber-heeler?’ The phrase usually applied to policemen, sent to check on another policeman.
[UK] ‘Metropolitan Police Sl.’ in P. Laurie Scotland Yard (1972) 327: rubber heel: internal police investigation (in contrast to the noisy steel-tipped heel of the traditional police boot).
[UK]J. Morton Lowspeak.

3. (US prison) in pl., meatloaf [negative comment on the dish’s consistency/flavour].

[US]N. Algren Man with the Golden Arm 208: ‘Rubber heels and fisheyes again’ was the word on the meatloaf and tapioca.