如果字符串的前面没有某些字符，我该如何匹配？

I've created the following regex pattern in an attempt to match a string 6 characters in length ending in either "PRI" or "SEC", unless the string = "SIGSEC". For example, I want to match ABCPRI, XYZPRI, ABCSEC and XYZSEC, but not SIGSEC.I've created the following regex pattern in an