Q:

Getting Sign Here URL by API which is sent in email

We are using docusign API to ask signer for signature via Email. We analysed the URL and found that it has two query parameters('a' and 'er'). Is there a way to get these two param pragmatically using API which can be used to generate runtime URLs?

A:

Yes you can generate direct URLs to use for sending and signing documents through DocuSign, but you don't grab it from the request emails that you are talking about - it's a completely separate process.  What you want is a feature in the DocuSign platform known as Embedding.
With Embedding you can generated authenticated URL "tokens" that can be used only once and they must be used before they expire in 5 mins and you have to generate a new one.  To generate a URL for a given recipient, though, you need to add them to the envelope in a slightly different way.  You need to set their clientUserId property along with their email and name, and then refer to that same clientUserId, email, name combination when requesting a signing URL for them.  
For instance, if you were creating an envelope from a template and wanted to use Embedding to generate a signing URL then you could use the following request body to create the envelope:
{
"accountId": "221765",
"emailSubject": "Hello World!",
"emailBlurb": "This comes from PHP",
"templateId": "9347C7AF-7EEE-4CEC-BA19-2734986F5501",
"templateRoles": [
    {
        "email": "test@gmail.com",
        "name": "John Doe",
        "clientUserId": "1001",
        "roleName": "Signer1",
        "tabs": {
            "textTabs": [
                {
                    "tabLabel": "address",
                    "value": "123 Main St. SF, CA"
                },
                {
                    "tabLabel": "zipCode",
                    "value": "94043"
                }
            ]
        }
    }
],
"status": "sent"
}

Then you could use the following request body to generate the signing URL for a given recipient.  Notice how the clientUserId (along with their email and name) matches from when we created the envelope:
{
"returnUrl": "http://www.docusign.com/devcenter",
"authenticationMethod": "None",
"email": "test@gmail.com",
"userName": "John Doe",
"clientUserId": "1001"
} 

The following page from the DocuSign Dev Center has detailed information on how to accomplish this (it's actually quite easy):
http://www.docusign.com/developer-center/explore/features/embedding-docusign
DocuSign also has two fantastic tools to help you test this and start coding it, the API Walkthroughs (which have sample code you copy out of the box, including 3 focused on Embedding functionality) and the API Explorer - which allows you to make any api call without writing a single line of code.  
DocuSign API Walkthroughs
DocuSign API Explorer

