You can certify each page of the Logbook with your personal signature. 

Read the User Guide how to set-up mySignature.  The User Guide is available here :  

Some pilots reported that the signature image is showing too small or too low, as illustrated here :

This is because the signature on the scanned image is too small.  Edit the image and cut-off the white area around your signature.  Make sure that the ratio of the image (width x height) remains 2 by 1.

The following illustration shows the entire area that is printed by mySignature.  Notice that the size of the image is not relevant.  Whatever image size you submit, small or large, it will always be shrinked to the printable area, as shown below.  So, what is important, is removing any white area around your signature.

The printable area stretches partially below the black line.  This is for signatures that contain lower characters, such as g,  j,  y...  If your signature is showing at or below the line and you want to get it higher, edit your image and move the signature upwards (add some white area at the bottom of your image).