KS59429 would be too old to be a Nishiki. That would be from when the brand was still being called American Eagle. The unorthodox character you're trying to identify is undoubtedly a numeral.

Photos probably wouldn't help much,if at all. The KS prefix puts it into a fairly narrow 3-4 year time range, when the bicycles didn't change much. The best bet to narrow things down would be component date codes, assuming they are OEM. For a guide on component date codes see Date of Manufacture of Bicycle Components can be used to date a bike: component dating