I'm sorry to tell this, but this does not look like his signature.
Search his signature on Google and you'll see only one type of signature and it is not this one.

Hi B_le_B :)

Thank you for your feedback {up} Great Success :P

You have been added to the list for the $10 gift certificate.

{star} [url=http://www.fanmail.biz/3574.html]Michael Fassbender[/url] on Fanmail.biz | [url=http://www.fanmail.biz/feedback/Michael_Fassbender.html]Previous Feedback Received[/url]

Fanmail 8)

To my eye, if you look at other examples of his signature online, these don’t look authentic. The letters don’t match... his M is different, for example. It can also explain why these are signed on the back.

It is so weird that Fassbender always signs the back of photos sent to him

I wrote a letter to Michael Fassbender and enclosed 2 photos,
as well as a game cover for a Nintendo Game Cube game,
on 25.07.2020 and received it today on 01.08.2020! [ugotmail]

This is the Address used:
Michael Fassbender
DMC Film
25 Atlantic Avenue
Ballycastle BT54 6AL
UK

I am very happy, even if it was signed on the back of the photos! {??}

[url=https://ibb.co/MnLqh1M][img]https://i.ibb.co/H7Qm2Pn/20200801-141942.jpg[/img][/url]
[url=https://ibb.co/VQKzP8c][img]https://i.ibb.co/rcWz1JR/20200801-141919.jpg[/img][/url]
[url=https://ibb.co/fdynhkQ][img]https://i.ibb.co/MktGYc9/20200801-141854.jpg[/img][/url]