tinypng-sigs

How do I use this option?

Do I setup the path like this? as a text file with .tinypng-sigs extension?

`	.pipe(tinypng({
		key: '99p7KPH2gMG00lzdrRHkRm0Fl2G135z5',
		sigFile: 'assets/img/.tinypng-sigs',
		log: true
	}))
`