UI Design – Representing Mandatory Fields ?

Currently, I am into revamping the UI of a retail product. The current version of the product is a based on client-sever architecture and has some watt inconsistent look and feel. Hence, I am into defining UI guidelines to bring about the much required consistency and to make it easy to learn (ie users must be able to self-learn the functionality without much help and without referring to on-line help)

One of the things on which we (I mean the team) are struck is how to visually represent mandatory field. Visual representation of mandatory fields is important because, if the user fails to define values for a mandatory field he will end up seeing pop-up error messages. This becomes even more cumbersome when the user leave more than one mandatory fields, in such a case multiple pop-up may have to be displayed.

Before we jump into the options let us look at how they are represented in products like SAP and Great Plains:

In SAP, the mandatory field is represented by a small tick mark inside the field. The good thing about SAP is the the tick mark disappears when a value is entered.

Whereas in Great Plains, the same is represented  as given in the image below ie the field labels are marked in ‘Red’ color and in italics:

Options such as making the field label ‘Bold‘ or  underlining the field label or using an asterisk at the end of label are some of choice we looked at. We even thought of giving a different color for the field (such as the outline or background). However, we are yet to arrive at a decision. My only concern about playing with the font properties of the field label spoil the look and feel. Having a tick mark similar to SAP is out of question as I am not sure if the same can be achieved using the technology used for developing the product

Any one encountered such a situation and any suggestions on what is a good way to represent mandatory fields’?