Your company must have issued appointment letter at the time of joining. In the appointment letter, they must have mentioned the various components of salary. You may show the appointment letter if your future employer asks for it. Most important is salary slip. You may show the salary slips for the last three months. That is the prevailing procedure.
You are free to show Gratuity amount as component of present CTC. nothinhg wrong in it. In a new organizations, your GRATUITY meter will be on ONLY after 5 years .You should show CTC break up while talking remuneration matters at salary negotiation before HR but no point when you report for joining. Because once remunerations part is frozen,offer issued , signed by you and company, nobody will listen.
I will go with the comments of Mr. Saswata Banerjee & Mr. R.D.S Yadav put together. It is true that you are free to put the Gratuity element while mentioning your Gross Salary in an application for a fresh appointment, but keep in mind that Gratuity is a payment against "Goodwill" that you create with your Employer. In case, whatsoever, if the Goodwill is broken, you Employer may deduct a part or may refuse to pay you Gratuity on cessation of service.