milepost

Short definition from Wiktionary

Noun

1. 1
   A post on a highway, often with one or more fingerposts, showing the distance in miles to nearby places.
2. 2
   A sign or post beside a railway marking the distance from the (actual or nominal) start of a line (usually the principal terminus or junction with a more major line).

Verb

1. 1
   To place mileposts along (a road, etc.).