Here’s an ad from the December 28 1926 edition of the Toronto Daily Star for a taxicab company that included a geometric proof.
I assume that Euclid was in the public domain, so De Luxe Cab Limited did not have to pay anyone to use his likeness in their ad. De Luxe Cab was at 108-110 Duchess Street in 1926 (Duchess Street later became an extension of Richmond Street East), but soon moved its main branch to 251 Queen East, remaining there down through the years.
This CBC article on the history of taxi service in Toronto describes De Luxe in more detail. It had started business in 1926 – the year of this ad – and held a virtual monopoly on the taxi business until the Great Depression.
The Depression reduced the number of taxi passengers and increased the number of taxis, as unemployed people with cars turned themselves into taxi services, all of which were competing for fares. The result was known as the Taxi Wars. This lasted until 1949, when ten taxi companies, including De Luxe, formed the Diamond Taxi Cab Association. Its headquarters was also at 251 Queen East; Diamond Taxi is still there today.