I don't travel much but when I do I always get a souvenir. I have come across souvenirs and wondered, should I keep this or what? I couldn't remember where or when I had got them unless it actually had a city or state or the name of a place I visited. I had more of those than anything. What is the longest that you have held on to a souvenir?
When I was younger, I started collecting Donald Duck Stuffed animals from every time I went to a Disney park. I ended up with about 4 or 5 of them and still keep them around my room. I don't think there's a designated time to actually keep a souvenir as long as it means something to you and brings back a good memory. In your case, if you can't even remember where you got it, then it's probably something you don't need to keep around.
Isn't a souvenir supposed to be kept for a life-time? I mean, you get one to remind you of a place you visited. Why would you want to part with it unless you've had a [recent] bad experience and you'd like to exorcise the memories of the place from your mind by getting rid of everything associated with it? Anyway, for me, like TJ, I don't get rid of my souvenirs. They're displayed in one room and shown to anyone who visits and wants to know what I've been doing.