The signal handler modification check is showing a signal handler change when there is none.

jcmd PID VM.info and hs_err reports contain this info. e.g.

$ jdk-19/bin/jcmd 17446 VM.info
...
Signal Handlers:
   SIGSEGV: javaSignalHandler in libjvm.so, mask=11100100010111111101111111111110, flags=SA_RESTART|SA_SIGINFO
    SIGBUS: javaSignalHandler in libjvm.so, mask=11100100010111111101111111111110, flags=SA_RESTART|SA_SIGINFO
    SIGFPE: javaSignalHandler in libjvm.so, mask=11100100010111111101111111111110, flags=SA_RESTART|SA_SIGINFO
   SIGPIPE: javaSignalHandler in libjvm.so, mask=11100100010111111101111111111110, flags=SA_RESTART|SA_SIGINFO
   SIGXFSZ: javaSignalHandler in libjvm.so, mask=11100100010111111101111111111110, flags=SA_RESTART|SA_SIGINFO
    SIGILL: javaSignalHandler in libjvm.so, mask=11100100010111111101111111111110, flags=SA_RESTART|SA_SIGINFO
   SIGUSR2: SR_handler in libjvm.so, mask=00000000000000000000000000000000, flags=SA_RESTART|SA_SIGINFO
    SIGHUP: UserHandler in libjvm.so, mask=11100100010111111101111111111110, flags=SA_RESTART|SA_SIGINFO
    SIGINT: UserHandler in libjvm.so, mask=11100100010111111101111111111110, flags=SA_RESTART|SA_SIGINFO
   SIGTERM: UserHandler in libjvm.so, mask=11100100010111111101111111111110, flags=SA_RESTART|SA_SIGINFO
   SIGQUIT: UserHandler in libjvm.so, mask=11100100010111111101111111111110, flags=SA_RESTART|SA_SIGINFO
  *** Handler was modified!
  *** Expected: javaSignalHandler in libjvm.so, mask=11100100110111111111111111111110, flags=SA_RESTART|SA_SIGINFO
   SIGTRAP: SIG_DFL, mask=00000000000000000000000000000000, flags=none

NOT in jdk-19-ea+6
IS in jdk-19-ea+7 and later

This is happending after:
8279124: VM does not handle SIGQUIT during initialization

In src/hotspot/os/posix/signals_posix.cpp

PosixSignals::print_signal_handler() prints the "Handler was modified!" text.
It checks if the saved expected action is non-null, not whether we have
do_check_signal_periodically[sig] == true

But although set_signal_handler has a parameter do_check, we always populate the SavedSignalHandlers vm_handlers even when this is false.