Magento – Change your store Logo Alt Tag via XML Layout Update
The beauty with Magento is being able to manipulate as much of your websites content as possible through XML Layout Updates – no need to create custom extensions for specific tasks and adjusting your Logos Alt tag is no exception either:
add the following to your CMS Page or Category Layout Update XML section through the Magento admin area (you can also in theory add this to your XML layout files).
<reference name="header"> <action method="setLogoAlt"> <value>Logo Alt Goes here!</value> </action> </reference>