Nice button!
It's from the Chicago Union Traction Co., founded in 1899. The lines originally included horse and cable trolleys, as well as electric ones. However, after 1906 all cars were electrically powered. The company was succeeded by Chicago Railways in 1908.
The maker of the button, Charles Rubens & Co. of Chicago, was active from 1883 until at least 1911, according to McGuinn & Bazelon. Tice cites a general range of late 1800's to early 1900's.
In the past, this button (cataloged as VanCourt # 47/18) has been listed at $20.