Can be used for SecurityType <167>=OPT to identify a particular security.
Valid values vary by SecurityExchange <207>:
For Exchange: MONEP (Paris)
L = Long (a.k.a. 'American')
S = Short (a.k.a. 'European')
For Exchanges: DTB (Frankfurt), HKSE (Hong Kong), and SOFFEX (Zurich)
0-9 = single digit 'version' number assigned by exchange following capital adjustments (0=current, 1=prior, 2=prior to 1, etc).