A small concrete post beside an old roadbed may look like forgotten building material. The letters on this one provide a more specific clue: SRD above R/W. Florida transportation documents use those abbreviations for State Road Department and right of way.
That makes a road-boundary marker a reasonable interpretation of the pictured object. Such markers can remain after vegetation obscures the route they once helped define. Their usefulness lies in their relationship to surveyed land and infrastructure, not in how prominent they look today.
The photograph does not establish this post's age, exact location or present legal effect. Those questions require the relevant maps and records. If an old marker interests you, leave it in place and use its lettering as a starting point for local historical research. A modest object can preserve a clue without answering every question about the landscape around it.
Sources: Florida Department of Transportation: Standard Abbreviations