What an interesting device! I've collected and looked at all kinds of curiousities but haven't seen this model. I agree it does not look like any other signal pistol. I'd want to stay openminded about its original intended function, maybe it was for firing cannons or something.
If I picked this item up, the first thing I'd do is examine the marks on it very closely as to whether the font, impression, tooling used to mark it, patination disturbance etc. really looked to be of the Civil War era or not. If you aren't an expert, take it to a couple of reputable, long-time antique gun dealers who will give an opinion. I'm a little suspicious of the markings myself, I just get the feeling they don't "go with" the piece.
The piece itself looks good, I don't think there's any problem with that at all, in it being an original "whatever" from perhaps 1850-1900. I'd think it was made during the earlier part of that period, but there may have been some special application for which percussion caps made more sense than cartridges, it is hard to tell.
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