Alternative advertising places your brand’s message in non-traditional locations, such as parking meters and bathrooms. Rather than relying on billboards or public transit, alternative advertising seeks out less common media to reach your target audience.

Alternative advertising can give you a distinct advantage over your competitors, exposing your company to new audiences in new places. With alternative advertising, creativity is rewarded, giving you the opportunity to make a memorable impression that can lead to a conversation. 

References

https://en.wikipedia.org/wiki/Alternative_media

http://www.murphymediagroup.com/ooh-media/alternative-advertising/

https://www.monash.edu/business/marketing/marketing-dictionary/a/alternative-advertising