Looks like a decorative whiskey flask to me, I don't it came filled and was just meant to be taken out and strapped to something while you walked the trail on your trusty steed...
I first googled "horseshoe cologne perfume" and found nothing similar. Then with epackage's thought on it being a whiskey flask I googled "horseshoe flask" and sure enough I found exact same one that was for sale at Etsy. Seller called it Kentucky green glass green glass flask, also says 1950's not much else. Unless you were the buyer I suppose you would of already of known that. I would post a link but I am not to good with these new fangled computers. Neat flask!Hope that helps.
I'd call it a novelty flask, meant to appeal to the horsey set. I do not think it has much age to it. I, too, agree that it's supposed to represent a stirrup.