XS_SECTION_SYMBOL_LEFT_ARROW_SYMBOL
Category in Advanced options dialog: Drawing properties
Use this advanced option to define the custom arrow symbol Tekla Structures uses as the section start symbol. To use a custom arrow symbol, select Custom from the Start list in the section mark properties.
By default, Tekla Structures uses the
symbol no 1 
in the
sections.sym file (located usually in the folder
\environments\common\symbols\). To use another symbol, enter
the symbol file name first, then the @ sign and then the number of the symbol, for
example sections@1.
Here's the symbol 0 selected in Symbol Editor:
To open Symbol Editor, click . There you can open different symbol files and check the included symbols and their numbers.
For more information about symbols, see Add symbols in drawings.
This advanced option is model specific and the setting is saved in the options database.