Hi Mario Dutra,
As our signatures are generated for us, we cannot change this, there is no option.
My workaround is to create either Hi, Hello, or whatever I would start the email with in Calibri font in blue, size 11 to match my email. I save the email several times as drafts on my PC/Laptop on Outlook. When I use my mobile, I go into the outlook email client and go to the Drafts folder. I copy this text, go into the inbox, click new email then paste this into the body.
This does not work for the next email if you go into the clipboard as this stores it as normal unformatted text. If you leave it a few hours after copying then it will not keep the format. You have to go back into your drafts folder
Unfortunately this is the only way it can be done.
Regards
Ste