You use block identifiers to mark blocks in a diagram that you want to find quickly. You can then use the Edit > Find and Edit > Find in Diagrams commands to find all blocks with the assigned identifier.
To add an ID to a block
1. Choose Edit > Assign Block Id.
2. Click the block to be assigned an identifier.
3. In the Assign Block Identifier dialog box, enter the identifier and click Assign.
4. Save the diagram.
To remove an ID from a block
1. Choose Edit > Assign Block Id.
2. Click the block whose identifier is to be removed.
3. In the Assign Block Identifier dialog box, enter the identifier and click Remove.
4. Save the diagram.