Select the apply now button that you would like to use. I have attached a default one you can use if desired.
Once you select the button download it and open it in Microsoft word:
Click the image select "Insert", then the "Link" option:
Once the dialog box opens, input your link as shown then select "OK":
You can confirm that the button is linked when you hover over the button and it shows the link:
You will then add the now linked apply now button image to your signature by click and dragging the image from Microsoft word to the Edit Signature box where you have your email signature email stored.