ECMS URL Parameters
From NewHaven Software Wiki
Some of the options in eCMS can be set using a URL parameter. Currently these include prom codes, price categories, and customer groups. A URL parameter is a string placed after a question mark at the end of your domain. You may want to use this for promotional material when offering a discount, this way a customer does not have to type in the promo code.
To set a promo code: http://www.domain.con/?p=promo_code_name
To set a price category: http://www.domain.con/?m=price_category_name
To set a customer group: http://www.domain.con/?c=customer_group_name