Hi Miros,
Do you mean that you want add signature to Outlook Web App? If so, create an email signature in OWA Office 365. To do this, please refer to the following steps:
1. At the top right of the Outlook Web App page, click on Setting
gear icon >click Options> Under the Options > click Settings> Mail.
2. In the E-Mail Signature box, type and format your signature. If you use both Outlook Web App and Outlook and want a signature in both, you need to create a signature in each.
3. To add your signature to all outgoing messages, select the "Automatically include my signature on messages I send" check box.
4. Click Save.
If I misunderstood rest of your Spanish words, please correct me and provide us detailed information (In English) about your issue so that we can further assist you to find a solution.
Best regards,
Shyamal