The department may immediately remove from any state highway any encroachment that:

1. (a) Is not removed, or the removal of which is not commenced and thereafter diligently prosecuted, prior to the expiration of five days from and after the service of the notice.
2. (b) Obstructs or prevents the use of the highway by the public.
3. (c) Consists of refuse.
4. (d) Is an advertising sign of any description, unless excepted by Section 670.