This button is sometimes described as a Queen Victoria era military/government. Well, it is and it isn’t …
According to the Victorian Button Collectors’ Club uniform button guru:
“I believe several government departments were able to wear a button with the reigning monarch’s cypher and appropriate crown. In Queen Victoria’s time Victorian Railways were lucky enough to have a button which seemed purposely designed for them. After her death the same lettering design was adopted and used with a KC for all of EVIIR, GVR and GVIR. It then continued with a QC under EIIR until the organisation changed its name. There can be small differences in design, seen when comparing buttons from different makers, and maybe sometimes even different time periods from the one maker.”
Victoria Collections confirms that ” These (buttons) were a standard form of button for police, railways and military during the Victorian era and in the case of the Victorian Railways until the 1960s.” https://victoriancollections.net.au/items/5f02ccaf21ea670df4a9c31d
Here is an example with a King’s crown (i.e. post 1901) which cannot be a “Victoria Regina” button, no argument, despite the similarity.
So to summarise: VR buttons with a QV crown (i.e. up to Victoria’s death in 1901) could be for Victoria Railways or another government department. However, with a King’s crown or Queen Elizabeth crown, only Victorian Railways.