Props, markings, and signals need to have an entry in the OpenDriveAssetData.xml file located in your Project folder in order to define proper "type" and "subtype" values for the corresponding <object> and <signal> entries.
In your case, you would need to add the following entries to the <Objects> section of the OpenDriveAssetData.xml file:
<Object>
<Type>roadmark</Type>
<Name>SolidSingle</Name>
<FilePath>Markings/SolidSingle.rrlms</FilePath>
</Object>
<Object>
<Type>roadmark</Type>
<Name>Stencil_LeftTurnArrow</Name>
<FilePath>Stencils/Stencil_LeftTurnArrow.svg_rrx</FilePath>
</Object>
<Object>
<Type>roadmark</Type>
<Name>Stencil_ThroughAndRightLaneArrow</Name>
<FilePath>Stencils/Stencil_ThroughAndRightLaneArrow.svg_rrx</FilePath>
</Object>
<Object>
<Type>pole</Type>
<Height>3</Height>
<Name>SignPost_10ft</Name>
<FilePath>Props/Signals/SignPost_10ft.fbx_rrx</FilePath>
</Object>
<Object>
<Type>roadmark</Type>
<Name>StopLine</Name>
<FilePath>Markings/StopLine.rrlms</FilePath>
</Object>
Note that my <FilePath> values here may be slightly different than the ones you use.
Similarly, you would need to add the following entries to the <Signals> section of the OpenDriveAssetData.xml file:
<Signal>
<Type>205</Type>
<FilePath>Signs/Sign_Yield.svg_rrx</FilePath>
</Signal>
<Signal>
<Type>206</Type>
<FilePath>Signs/Sign_Stop.svg_rrx</FilePath>
</Signal>
<Signal>
<Type>301</Type>
<FilePath>Signs/Sign_PriorityThroughTraffic.svg_rrx</FilePath>
</Signal>
Note, that similar to the <Object> entries, my <FilePath> values may be slightly different.
You can find further details on this XML file here: Export to OpenDRIVE - MATLAB & Simulink (mathworks.com)
