Small debug program for printing the ProcessInfoRec launching process' signature. When macOS starts a process automatically at login due to the "Reopen windows when logging back in" checkbox, the launching process' signature is "lgnw".

LauncherProcessSignature.m

#import <Foundation/Foundation.h>
#include <ApplicationServices/ApplicationServices.h>

//
// Given a single PID on the command line, print the process'
// signature and the launching process' signature. The process'
// signature is a field in the ProcessInfoRec structure.
//

// For converting the process signature 4 byte field to a string.
// Copied from https://stackoverflow.com/questions/14222435/ios-c-convert-integer-into-four-character-string
#include <TargetConditionals.h>
#if TARGET_RT_BIG_ENDIAN
#   define FourCC2Str(fourcc) (const char[]){*((char*)&fourcc), *(((char*)&fourcc)+1), *(((char*)&fourcc)+2), *(((char*)&fourcc)+3),0}
#else
#   define FourCC2Str(fourcc) (const char[]){*(((char*)&fourcc)+3), *(((char*)&fourcc)+2), *(((char*)&fourcc)+1), *(((char*)&fourcc)+0),0}
#endif

int main(int argc, const char * argv[]) {
    if (argc != 2) {
        printf("Usage: %s <PID>\n", argv[0]);
        exit (1);
    }

    int pid = atoi(argv[1]);
    ProcessSerialNumber psn;
    OSStatus error = GetProcessForPID(pid, &psn);
    
    ProcessInfoRec procInfo = {};
    if (GetProcessInformation(&psn, &procInfo) != noErr) {
        NSLog(@"GetProcessInformation() for PID %d failed.", pid);
        exit (1);
    }
    
    NSLog(@"This process: PID: [%d] signature: [%s] name: [%s]",
          pid,
          FourCC2Str(procInfo.processSignature),
          procInfo.processName);
    
    ProcessInfoRec parentInfo = {};
    error = GetProcessInformation(&procInfo.processLauncher, &parentInfo);
    if (error == procNotFound) {
        NSLog(@"GetProcessInformation() for process launcher failed: procNotFound");
        exit (1);
    } else if (error != noErr) {
        NSLog(@"GetProcessInformation() for process launcher failed.");
        exit (1);
    }
    
    NSLog(@"Launching process: signature: [%s] name: [%s]",
          FourCC2Str(parentInfo.processSignature),
          parentInfo.processName);
    
    exit (0);
}