I worked in a card and gift store for over three years, and in that time there were many things that happened that makes me believe in ghosts.
This was about three years ago, soon after Christmas when the "major" incident occurred. We had just switched all our cards and merchandise from Christmas to Valentines Day, and at 10:00pm, me and my co-worker set the alarm and walked out the door. It was a Saturday night, and I went to a friends house. Around 1am my pager went off, the mall security number. I called them back and they said I needed to come back to my store, our alarms were going off.
I went to the store, thinking that balloons that we put up that day might have set off the alarms. I went in, and pulled the balloons down, called our store security team and went to reset the alarm. When I set it, the alarm defaulted, saying there was a motion in the front of the store. I hit clear and set the alarm again. It defaulted again saying a back motion was detected. It was about 1:30am, I was alone and getting scared. I called our security team and they said they would override the alarm. I took one last look around, and the store looked normal.
The next day when I came to open the store, there was a stuffed animal sitting on the ground, with a box of chocolate on it's lap, an "I love you" card beside it and a chocolate rose in front of it. It had not been there the night before. When I walked behind the cashwrap, I jumped back in surprise. The step ladder had been opened and set across the register area so that the only way around it was to close it, and all the balloons I had pulled down the night before were popped. The register keys where laying on the floor, and the drawer they were kept in was open.
I high tailed it out of there, locking the door behind me and got a security guard. We opened the store and went through it together, there was no one in the store. The only way in and out of the store was if you had a key, the backdoor would only open with a key, or the alarm would go off, and the only way to turn the alarm off was to put your key in. It was a fire alarm door (which we checked and worked). I called the alarm company and they said the only time the alarm was cut off during the night was when my code was entered at 1:16am, and reset in override at 1:49am.
Many times before and after that night, if we were working late we would hear footsteps in the storage alcove above our backroom, you could go upstairs and no one would be there.
Sometimes you would be upstairs and hear footsteps on the stairs, and when you looked, no one would be there. There was also this one wall, that every time I was near, someone would come up to me and touch my arm, only when I turned around, I was alone. When I told my current boyfriend the story he laughed at me and told me I was crazy, but he works security in the mall now, and sometimes has to work overnight. He believes me now, because many nights he has seen things move in the store, or has heard voices.
One night 6 of us were putting up a barricade on a storefront that was being remodeled, and we heard one of the motion singing fish go off, only no one was around. I am not sure why, but that store is definitely haunted.