snc/force_login_screen is a SAP Parameter attribute which is used to control Display login screen for each SNC-protected login information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
If this parameter is set to "1", the logon screen is definitely
displayed for a logon secured with SNC (Secure Network Communications).
If the parameter has the default value "0", the logon screen is skipped
if exactly one client contains exactly one R/3 user, and the SNC name or
external name provided during the SNC logon is assigned to this user.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.