On a phone, Flarum's navigation bar carries a menu button and nothing else. Someone arriving on a discussion from a search result has no indication of whose forum they are on. This puts your logo there.
composer require linkrobins/mobile-logo
Installing does not switch it on. Enable it:
php flarum extension:enable linkrobins-mobile-logo
It then uses your favicon straight away, so there is nothing else to set up unless you want something different.
What it does
- Shows an image in the mobile navigation bar, beside the menu and back buttons. You choose which side.
- Uses an image you already have. The favicon by default, because a favicon is square and square is the shape a navigation bar has room for. You can point it at your forum logo instead, or at any image address.
- Taps through to the homepage, the way the logo does on desktop. You can turn that off and leave it as decoration.
- Stays out of the way on desktop, where the header already shows your logo.
What it does not do
- It does not replace your header logo. Only the phone navigation bar changes.
- It does not crop or reshape your image. A wide wordmark scales down to fit the height and can end up small. If that happens, use a square mark, which is what the favicon option is for.
- There is no per-user setting. What you choose is what every visitor sees.
Settings
Admin, then Extensions, then Link Robins Mobile Logo.
- Which image to show: favicon, your forum logo, or a custom address.
- Where the logo sits: left or right of the menu and back buttons. Right leaves those buttons against the screen edge, which is a slightly easier thumb target.
- Height in pixels: 16 to 64, default 32.
- Tapping the logo goes to the homepage: on by default.
If the image cannot be shown, nothing is shown rather than a broken image. That covers an address that is not usable, a file that has gone missing, and a plain http:// image on an https:// forum, which browsers block.
A path on your own site such as /assets/my-logo.png is best. A full address elsewhere works too, but that host then sees every visitor who loads a page.
Where this came from
The idea is a CSS tweak posted by 010101 on the Flarum community forum: 
#27333
That tweak draws the logo with an ::after on the navigation bar, and it still works on Flarum 2.0. If a fixed image is all you want, it remains a perfectly good five lines of CSS and you do not need this.
This extension exists for what a pseudo-element cannot do. It renders a real image, so the logo can link to your homepage, which was the most-asked question on that thread and never got an answer. It carries alt text, so screen readers announce it. It reads the image from what your forum already has instead of a hardcoded address. And the size is a setting rather than three CSS values you tune by hand.
Requirements
Flarum 2.0 or later, and PHP 8.3 or later.
Source and issues: linkrobins/mobile-logo
Reply here or open an issue.
