reply to u/Deep-Seaworthiness48 at https://www.reddit.com/r/typewriters/comments/1e5gh4p/two_5_keys_sc_poweriter/

Things like that happened on alternate language/region typewriters. I've got a Dutch keyboard layout that repeats a % symbol twice.

It's likely that the pound symbol was needed/required so they pulled one from a pre-existing typeslug and key cap on a keyboard where the £/5 key was common and replaced the 1/! which in the era was widely known could be done by alternate means (aka lower case 'l' and '.' backspace '''.

The value of the £ was more important to the typist and because of typeface manufacture was probably easier to do in the £/5 existing combination from something like the English No. 1028, International No. 1060 keyboard, the Brazilian No. 1065, or the Danish No. 1047 all of which paired the £/5. See also: https://munk.org/typecast/2023/02/03/1954-smith-corona-scm-typewriter-type-styles-and-keyboards-catalog/

Off hand, I don't see another S-C keyboard combination from that time period that had a £ paired with any other glyph/character. In the "change-a-type" time period they likely wouldn't have done a custom black key for the £/5 when they were already manufacturing one in a matching white. If they didn't also swap out the key at the far right end of that bank, I would expect it to be a standard black '+/=' key cap and slug.