Tally gives you the option of selecting a customer source letting you record how you acquired this customer. This can be used for reporting purposes and is particularly useful in monitoring where you are getting most of your business from. This could be from referrals, advertising campaigns, partner companies etc.
By default, a customer source called 'Other' is set up for you. You can add another source by going to Customers > Click Sources button. On the next screen, using the text boxes enter in the source name (i.e. trade show) and a source cost if any (without the currency symbol), then click Add. Please note that any source cost will not be reflected in your accounts and is only for reporting purposes. When you've added your source you can now assign customers to it by going to Customers > Select a customer > Options > Use source drop down to pick a source.