According to this page on the Tigertronics website you can’t do FSK with the Signalink.

Of course you can, you just have to be a little creative…

Use the Signalink for RX and make this interface from Don AA5AU’s site for keying your transceiver.

It takes only a few euros and a few minutes of work for the hardware.

Configure MMTTY for transmitting FSK through your serial port et voilà!