Here are two advertising covers. The first is a promotion for Chase Brothers, a nursery and seed company in Rochester, NY. It is posted with two US Scott 206 with a Dec 17, 1883, Rochester cds.
The second is more interesting to me. It's a template ad promoting the Wisconsin State Semi-centennial celebration in Milwaukee, which took place from June 27 to July 2, 1898. The cachet depicts the Milwaukee City Hall; a figure that I believe stands for "Forward," which is the Wisconsin state motto; and, to add a little whimsy, a clown and a policeman (partially cut off) where the stamp is affixed. A number of companies used this cover to promote themselves. This one was sent by Kersting & Apel Co., a short-lived Milwaukee-based importer and market maker of coffee and teas. It's posted with either US Scott 252 or 267 depending on the watermark. The date stamp is a Barry machine cancel with an oval postmark and diagonal line killers. The bottom photo is of the upper right of the back of the cover. You should be able to make out the pin impressions, which is a hallmark of a Barry machine cancel.