Hello,
It is possible to add a link to a signature, but it is not possible in the current Yahoo Mail to insert an image into your signature.
If you really want an image in your signature consider switching from the Yahoo webmail to a mail program on your computer such as Mozilla Thunderbird. Thunderbird can be configured to
access your Yahoo account over an IMAP connection. You will be able to read and send as your Yahoo mail account, but it requires that you use a mail program on your computer instead of using the Yahoo web page.
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