Missouri Revised Statutes Title XXXVIII. Crimes and Punishment; Peace Officers and Public Defenders § 569.145. Posting of property against trespassers, purple paint used to mark streets and posts, requirements

(1) A vertical line of at least eight inches in length and the bottom of the mark shall be no less than three feet nor more than five feet high. Such marks shall be placed no more than one hundred feet apart and shall be readily visible to any person approaching the property; or

(2) A post capped or otherwise marked on at least its top two inches. The bottom of the cap or mark shall be not less than three feet but not more than five feet six inches high. Posts so marked shall be placed not more than thirty-six feet apart and shall be readily visible to any person approaching the property. Prior to applying a cap or mark which is visible from both sides of a fence shared by different property owners or lessees, all such owners or lessees shall concur in the decision to post their own property.

Posting in such a manner shall be found to be reasonably likely to come to the attention of intruders for the purposes of section 569.140.