If your great grandfather (and/or the sign) was the focus of the photo, it seems a bit odd that he isn't seated in the middle - though you could also argue that by the rule of thirds, his position in the asymmetrical grouping is just as much the focus of the picture.
Interesting about the Butchers Charitable Institution. Was he son of Roland and Theresa, in 1881 census at RG11/3925 fo66 p34? If so, then his father was a butcher's assistant, so once orphaned, he might have been eligible for assistance there.
Can anyone narrow down the date based on what the guys are all wearing? I'm currently wondering if the picture might be of people from the institution, to mark his leaving or coming top in a exam etc. If he had been there, I suspect he would have left before getting married (in 1899).
I see the institution's records are at London Metropolitan Archives (ref. CLC/117):
https://search.lma.gov.uk/scripts/mwimain.dll/144/LMA_OPAC/web_detail/REFD+CLC~2F117?SESSIONSEARCHClick the Level Down button at the bottom to see all the individual items in the collection.