On a recent trip through London, I noticed a rather large piece of signage at Holborn tube station. Each letter was at least 4 inches high.
The style of the signage was reminiscent of that found on motorways, where huge signs are used to give drivers advanced notice of any important messages. I believe the tube station had adopted the same approach as part of a user experience effort to reduce confusion and danger as passengers travelled through the station. By having the signage so large, passengers would be able to read which direction they would need to go from a long distance away. They would then not need to slow down as they approached the gangway in order to find out which route they needed to take, which would cause congestion, and could potentially be dangerous.
It is common to see on various means of public transport queues of people waiting to read directions or wayfinding devices. If the wayfinder is small, then only the person directly in front of it would be able to use it. With the use of bigger signage then multiple people can use it at the same time, and would also not need to get so close in order to make use of it. Resulting in fewer people gathered at one place, and an increase in the flow of traffic through the area.
Not only is it good for those who are unfamiliar with the station or the tube network, it is also useful for those who have visual impairment.
The implementation of this is particularly useful at such a busy thoroughfare, filled with tourists who would take longer than a regular user to figure out where they need to go. The fewer irregular tube users gathered around small signs, the easier it will be for those who do not need to read the signage to pass by, onto their destination.