Southern Precision Instruments Company Incorporated
I don't know that they are in business anymore. The website they have is very outdated and only mentions their microscopes and telescopes. No mention of rifle scopes. If you look at the logos on their other products, it matches the logo on my SPI rifle scope (that I purchased used with no paperwork). The logo is a diamond with an SPI in the diamond.
A sample picture of the logo on a telescope can be found below:
http://www.cloudynights.com/ubbthreads/attachments/2036141-SPI_Focuser.jpg
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