Mari 4.5v2 docs:

Status Bar

The status bar and descriptions of all the controls on it can be found in the tables below.

Note: The status bar also displays basic tool help for the current tool.

What it looks like	What it does
	Displays status icons that indicate which features are active, whether an error has been encountered, and information about the current project. This includes progress bars on running processes.

Status Bar Icons

Icon	What it does	Notes
	Displays the UDIM number of the patch you have selected. If nothing is selected, then there is nothing listed after Udim.
	Notifies you that there is paint to bake.	Click on the icon to bake.
	Notifies you that background jobs are currently running.	Clicking on this icon displays a dialog for the progress bar.
	Notifies you that the project has changed and allows you to save.	Click on the icon to save changes.
	Notifies you that your painting is hidden.
	Notifies you that you are currently projecting on the front of objects.	Clicking on this icon toggles between projecting through objects and projecting on the front of objects. The icon takes the default icon’s place when switching to project through.
	Notifies you that you currently have edge masking enabled.
	Notifies you that you currently have channel masking enabled.
	Notifies you that you currently have ambient occlusion masking enabled.
	Notifies you that you currently have depth masking enabled.
	Notifies you that you currently have backface masking enabled.
	Notifies you that you currently have fractal noise masking enabled.
	Notifies you that you currently have the global mask preview enabled.	Clicking on this icon disables the global mask preview.
	Notifies you whether you are in LDR (Low Dynamic Range) or HDR (High Dynamic Range) mode.	Clicking on this icon toggles between LDR and HDR. When in HDR mode, the icon appears as .
	Warns you that a low memory status has been detected. Low memory affects Mari’s performance and may make it unstable.	Try freeing memory or closing and restarting Mari to clear this issue.
	Notifies you that there are warning messages present.	Clicking on this icon displays these warnings.
	Warns you that the cache disk is critically full.	If you don’t free disk space, data loss may occur. A simple way to free disk space is to close the project and re-open it. Mari saves your session history, but closing your project clears this used disk space up for use.
	Warns you that there is no disk space left for the operation you are trying to run.
	Warns you that channels are a higher bit-depth than what the virtual texture is configured for.
	Notifies you that Mari is currently loading data from the disk.
	Notifies you that Mari is currently loading data from the RAM to GPU memory.
	Notifies you that Mari is listening for commands on [COMPUTER NAME] port [PORT NUMBER].	Hovering over this icon displays the computer name and port number on which Mari is listening for commands.
	Notifies you that there was an error while Mari was listening for commands.
	Notifies you that Nuke is connected to send commands to Mari on [COMPUTER NAME] port [PORT NUMBER].	Hovering over this icon displays the computer name and port number from which Nuke is connected.