Green’s Dictionary of Slang

1. (US) an inquisitive person.

1902		C.L. Cullen More Ex-Tank Tales 10: Far be it from me to accuse the whole outfit of being natural-born rubberers.
1925		N. Lucas Autobiog. of a Thief 224: ‘Blime,’ said a bystander, a ‘rubberer,’ as he would be called in New York City.
1939		Dly Herald (London) 4 Aug. 15/3: No man [...] can escape the gaze of the Rubberer [...] These devotees of curiosity sarm like flies [...] about the scene of an unusual occurrence.

2. a tourist.

1906

Goodwin’s Wkly (Salt Lake City, UT) 15 Dec. 10/2: Oh my; that rubbering rubberneck with his bunch of dummy rubberers, in the Seeing New York car.

3. (US) a peeping Tom.

1909

Hawaiian Star (Honolulu, HI) 10 Dec. 8/3: The ‘rubberer’ when he had looked long enough through one window, moved [...] to another. Wright donned some clothing and hastened out to grab the fellow; rang for the patrol wagon and sent ‘Peeping Tom’ to jail.

4. (US) one who eavesdrops on a party-line telephone call.

1914		Wash. Herald (DC) 19 July 25/3: Phone ‘Rubberer’ is Doomed [...] The ‘rubberer’ is a felon of the past [...] a telephone exchange [...] has invented an indicator which will point out the ruffian who butts in on a personal call.
1920		Richmond Times Dispatch (VA) 20 Apr. 34/2: [headline] Reasons Why Party Line Rubberers Should Not be Shot.