The rule for annotations is to always annotate at the bolt on the pole. If arms are present, you can start by clicking at the bolt and searching for the "arm" input. You may need to switch to the "measure" photo toolset before annotating in your first photo. If performing PLA you will need to select the correct arm spec attribute from the dropdown.
*The arm input may need to be configured in the model editor to include the arm spec attribute. You can update it for your model or manually add the attribute by clicking the three dot menu in the top of the marker and then "add +" and adding arm spec.
Crossarms are more centered on the pole and can come in different lengths. They can be single or double as well.
Alley arms are offset from the center but also come in singles or doubles and can be different lengths.