How do I show different Custom Registration Fields for each Signup Form?
Each Custom Registration Field can be assigned to a specific Membership Level, so that it only shows up on Pro-Forms for that particular Level. For example, if you had one set of Custom Registration Fields that were applicable to Level 1 memberships and another set of Custom Registration Fields that were applicable to Level 2 memberships, you could create your Custom Registration Fields and set the Applicable Level.
See: WordPress Dashboard → s2Member (Pro) → General Options → Registration/Profile Fields & Options → Add New Field
By default, each Custom Registration Field will appear on Pro-Forms for
all Membership Levels, but you can customize this as needed. If you want the Custom Registration Field to appear on several Membership Level signup forms you can separate each level with a comma. For example, to show a particular field on Level 1 and Level 3 signup forms, you would enter
1,3 in the Applicable Membership Levels field.