What is the most reasonable way to have a custom logo in a policy product in Plone 5? Using something encoded inside XML for plone.site_logo in registry seems painful, using portal_skins is doable, but is there not a way to use a URL to a static resource?
I'm not looking to do this in Diazo, because I have multiple sites, each with their own policy, but sharing a single theme.
Sean
Doesn't answer your question but it is possible to have subthemes where you include the diazo from a shared base theme. Although from memory it had some annoying limitation like share resources like CSS or something similar 
Can't you just override the logo viewlet in your theme ?
I use the "registry way" via encoded xml. It's not painful, perhaps overelaborate.
<record
interface="Products.CMFPlone.interfaces.ISiteSchema"
prefix="plone"
field ="site_logo">
<value purge="False">filenameb64:...;datab64:....</value>
</record>
That is my likely direction; one of the add-ons all these sites share already overrides the logo viewlet for a different purpose (TTW subsite logos), so I suppose extending what I already have to support a resource URL stored in registry is the logical conclusion (would be nice to see that OOTB some day, though, as alternative to stuffing a base64-encoded image in registry.xml).
Sean
According to the code, when site_logo is set to empty value, "logo.png" from portal root is shown. So, setting empty value and creating /logo.png using GenericSetup's structure import should work.
Any downside for including z3c.jbot and adding a plone.app.layout.viewlets.logo.pt (where you could define logo src url) or a more directly Products.CMFPlone.skins.plone_images.logo.png to its overrides folder?
Hey this is fun.
I've tried that with the base64 encoded Plone SVG Logo from here: https://upload.wikimedia.org/wikipedia/commons/d/df/Plone-logo.svg ... b64encoded filename: plone_logo.svg ... result in my policy registry.xml:
<record name="plone.site_logo">
<value purge="true">filenameb64:cGxvbmVfbG9nby5zdmc=;datab64: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</value>
</record>
et voilá 
I've used this converter: SVG to Base64 | Image | Base64 Encode | Base64 Converter | Base64
PS: I think SVG support needs Plone6 coredev buildout ... but maybe works in latest 5.2 too
If you add the logo manually, I think SVG works (I am pretty sure I have done this once)
UPDATE: In Plone 5.2+