According to ISO 15118-8 (developed jointly with IEC):

SECC shall include a Vendor Specific Element in its Beacon frames and Probe Response frames

From the hostapd.conf man page

# Additional vendor specific elements for Beacon and Probe Response frames
# This parameter can be used to add additional vendor specific element(s) into
# the end of the Beacon and Probe Response frames. The format for these
# element(s) is a hexdump of the raw information elements (id+len+payload for
# one or more elements)
vendor_elements=dd1170B3D531900204