Much like road signage, advertising the location of a business park gives people travelling to the local area help in finding a business. It also demonstrates to existing and potential tenants that the site is well maintained and advertsied.
Also having business premises empty could be losing you valuable revenue so advertising any vacancies with external signage to the site is a cost effective way of ensuring people in and about the local vicinity are aware of its location and any availability.
Large Business Parks are often owned by large property investment companies and thus don’t have the usual restrictions with regards to signage size or placement. These are examples of a large road side hoarding overlooking a main road and upon entrance to the business park.