Pegged transfer from private blockchain to sidechains - Issue
The secondScriptSig is a script in each transfer transaction which satisfies the chain-global secondScriptPubKey. The secondScriptPubKey is intended to allow, in a flexible way, each chain to define its own additional terms. For example, a chain may restrict transfers to only be allowed if they are co-signed by a multisig federation (in the full federated peg mode), or restrict the total value which may be pulled out of a sidechain in individual transfers. In alpha, it is effectively unused - hence the secondScriptSig simply being the constant script "OP_TRUE".