"Advertisement Placement Agreement" for 広告物設置契約書.

I think that just "Advertisement Contract" is fine for the term you inquired about.

If 設置 is in there, then add either "placement" or "installation." Also, if the two terms refer to the same contract (which they probably do), then keep the word "contract" for both.

If they refer to different contracts, the difference is probably that the general "advertisement contract" determines the content (colors, characters, style) and types of ads (poster, wall ads), and the "advertisement installation agreement" determines locations, responsibilities, time and methods for actually placing the ads. This is just a guess, though.

I must admit that I don't know the broader context of this translation. However, as somebody who does a lot of marketing research translation, advertising translation, in the context of those two areas 広告物 are often referred to as advertising materials. For example, point of purchase materials (stickers, pamphlets, etc.). This term might also be used to apply to a range of different advertising materials across different media (for brand stability) such as printed ads, POP material, flyers, etc.