Just to be 100.00% clear (and rather anal about it), the S&W trademark "Accu-Guide" (or "Accuguide") and the patent for certain improvements in magazine design (mainly related to accommodating more powerful cartridges including the .40 and 10mm) are two separate things.

Here is the trademark: ACCUGUIDE Trademark of Smith & Wesson Corp.. Serial Number: 74020716 :: Trademarkia Trademarks

Here is the relevant patent: Patent US5014456 - Cartridge magazine for semi-automatic firearms - Google Patents

The trademark didn't depend on the patent or vice versa. But it's pretty clear looking back that someone at S&W must have felt that a trademark needed to be applied to its improved magazines for the first time in S&W history. Why? I have no idea.

Note that S&W did not hold onto the trademark for very long and it is now owned by an unrelated company.