What Marine wouldn't have one? 
The Jewel of my collection came as a gift from a friend I had done a number of favors for, not expecting anything in return. He was an older gentleman, with a number of medical problems and needed help. So, I helped. I wasn't gimpy then, and could. He called one day and asked if I could stop by, he had found something in a yard sale for me...
He gave me this:
He said he saw it as the woman laid it on the blanket, asked her how much. She said, "Twenty Bucks." He told her he had Thirteen bucks in cash or could write her a check. "Thirteen it is."
I did some research and found this information.
One of 700 Navy Spencer*s ordered with sword bayonets. This one is #150, which is stamped into the butt end of the hilt. It is marked Collins & Co. Hartford Conn. and dated 1861 on the other side. The hilt is Excellent. The blade is mostly bright with some gray areas. The leather scabbard is excellent but the drag is missing. A full article on The Spencer Navy Rifle by Rollin Davis can be found in Gun Report, Aug 1974. See also US Sword Bayonets 1847-1865 by Rollin Davis, Jr., MD., BSME
The Collins and Company Spencer Bayonets at the time were selling for about $600. I offered the Bayonet back to him. "It was a gift. If I bought a lotto ticket and gave it to you and it won, I wouldn't ask for it back. Besides, all your help has been priceless. Enjoy." He laughed at me later, because HE knew I wouldn't sell it.
I checked recently, these things are going for upwards of $1,000; and sell quickly. Those in the low numbers especially. Mine IS in the low numbers. I can't remember now what the Serial Number is, but it's in the lower half of the 700. I'd check, but the safe it's in is in the room where Miss T is sleeping.
