Accredited investors meet standards defined by the US Securities and Exchange Commission which allow them to invest in certain private securities offerings. Most startups raising money do so from accredited investors only.
The SEC web site contains the full definition. In general, any of the following would meet the standard:
In order to fulfill the accreditation requirements with your crypto-asset holdings, you can either
In either case, you will also need to provide documentation of your debts (e.g. via a credit report or letter from your accountant) in order to qualify.
I, <Signatory Name>, certify under penalty of perjury that <Investing Entity Name> is the sole owner of the cryptocurrency address associated with this message as of <Today's Date>.
Replace the angle brackets with your name, the name of the investing entity, and the date.
For Ether, use MyEtherWallet's message signing tool
Paste the message into the text field.

Select your wallet provider. (In this example, we use MetaMask.)

Click 'Connect'. Then, click 'Sign Message' to sign and approve the transaction. (There is no cost.)

Here is an example signed message:

For Bitcoin, most wallets implement the ability to sign a message with your Bitcoin address’ private key. See this tutorial about how to sign a messaging with a blockchain.info wallet. See here for Jaxx wallet.
Create a document with the message you signed, address, and message signature (sample information provided below):
A. Message:
I, John Smith, certify under penalty of perjury that I am the sole owner of the cryptocurrency address associated with this message as of Dec. 13, 2017.
B. Address
1UsRE3sak3u7qNaQ8Y1X4UmQS93qruLMt
C. Signature
IEXlF8laYLp1ZdQbIxWcXvQdt7d/0TyKLqKMNoTdpqCXG7LLm6upe4wjl6q9ZAtHc4paw9LqP8CudBNyOEwt1mo=
You can upload this information via the CoinList sale registration process or log a support ticket in our Support Center.
In the event that your funds are spread across multiple wallets, you will need to include a signed message from each address.
Also, remember to provide documentation of your debts (e.g. via a credit report or letter from your accountant).