Symbol 6321 from IEC 60417 - Title/Meaning: Resistor, general; series device Function/description: To identify the two-terminal device characterized essentially by its resistance.[]On direct acting indicating analogue electrical measuring instruments and its accessories, to identify the accessory to be connected in series with the voltage circuit of a measuring instrument in order to extend its measuring range.
Additional information: 
In the application of this symbol, the letter symbol either R, L, or Z is placed within or adjacent of the rectangle to identify the type of accessories, series resistor, series inductor or series impedance, respectively.
Own work using: iso.org/obp/graphics/grs/4d93d14e-708c-4937-aa30-b3c41d47c048 200.png
Vectorization:  Mrmw