Minn. Stat. § 219.17: UNIFORM WARNING SIGNS.

The commissioner by rule shall require that uniform warning signs be placed at grade crossings. There are four distinct types of uniform warning signs: a crossbuck sign, for use in the immediate vicinity of the crossing; an advance warning sign, to indicate the approach to a grade crossing; a yield sign with the word "yield" plainly appearing on it; and, when deemed necessary and instead of a yield sign, a stop sign with the word "stop" plainly appearing on it, to indicate that persons on the highway approaching the crossing, whether in vehicles or otherwise, must come to a stop before proceeding over the grade crossing.