warning: negative value in unsign

static U32 signature[SIGNATURESIZE+SIGREGISTSIZE] =
                                                           {0x1234,0x5678,0x8765,0x4321,0xFF00,
                                                                   0,-100,-100,-100,-100,-100,-100,-100,
                                                                -100,-100,-100,-100,-100,-100,-100,-100,
                                                                -100,-100,-100,-100,-100,-100,-100,-100,
                                                                -100,-100,-100,-100,-100,-100,-100,-100
                                                           };

//=************************ Dev_CheckSignature *********
//=*****************************************************
S32             Dev_CheckSignature( U32 pid )
{
        if( signature[SIGNATURESIZE] != 0 )
        {
                int             i;

                for(i=0; i<SIGREGISTSIZE; i++ )
                {
                        if( signature[SIGNATURESIZE+i] == pid )
                                break;
                }
                if( i>=SIGREGISTSIZE )
                {
                        Dev_Printf( BRDdm_VISIBLE, CURRFILE, "<CheckSignature> Unregistered Board PID:%d(0x%X)", pid, pid );
                        return -1;
                }
        }
        return 0;
}