In this repository you can find the source code for both Signals Pre-Sale and Main Sale smart contracts.
https://etherscan.io/address/0x25b16c95f3ebb1d8583a1c173f81257bc916a9be#code
Please be aware you need to register prior sending any Ether to the smart contract address, otherwise your transaction will be rejected.
https://etherscan.io/address/0xB2135AB9695a7678Dd590B1A996CB0f37BCB0718#code