I've received great advice and answers to questions here in the past. Hoping for an answer to this one . . .

Last weekend I looked at a Charles Daly O/U made by Miroku. 28 inch tubes, 12 gauge. When you break the action you can see that the ends of the barrels are marked inside (i.e. on the part of the barrels that's hidden when the gun is closed) with a series of plus and minus signs. My common sense tells me these must be choke markings, but I haven't been able to find an answer to what they mean.

The top barrel is marked + (that's one plus sign) and the bottom barrel is marked + + - (that's two plus signs and one minus sign). Anybody know how to interpret these?