Slot & Plug Weld Symbols - Weld Guru
The spot weld symbol is simply a circle that may be placed above, below, or centered on the reference line. When the symbol is centered on the reference line this indicates that there is no side significance.
AWS A2.4:2020 Welding, Brazing, NDE Symbols Standard
If the designer wants the hole or slot to be partially filled, the depth of filling is mentioned inside the weld symbol.
Tutorial Creating Plug and Slot Welds in Creo Parametric - Creo
Arrow Side & Other Side Indication of a Slot or Plug Weld Symbol.