In Settings > Hub and Members, you have the option to set an automatic welcome message to all new people who signup to join your community.
To send the message, check the box to "Send to all new community members when they're accepted." Whenever a new volunteer fills in your general signup form or signs up for an event, assignment, gathering, they're sent an email to verify their submission. You're then given the opportunity to manually approve these people (which adds them to your community), or you can set your activities and membership to automatically accept all volunteers once they've verified their email.
Once accepted, either automatically or manually, the volunteer will be added to your Community Directory and sent your Welcome Message. The Welcome Message email includes your organization logo, name, and your personal message.
You can edit the text of your welcome message, format the text, and add links.