In India the registry would recognize a trademark as a well-known trademark, based on its national and international market presence and cross border reputation.
When a mark has become a significant part of the public and the goods and services they are associated with, has a reputation and is recognized due to their association with certain goods/ services can be called well-known marks.
Here as matter of, if we talk about lays, people associate lays directly with potato chips. It is a brand that has both national and international market presence. Hence no one is permitted to use the trade name Lays for any other goods/ services. This is to avoid any illegitimate use of the brand and secure its reputation. Also, consumers are at a high risk of being misguided if Lays is used for any other goods/ services. It is obvious for them to assume that the company that owns lays has started out a new venture
Hence it can be called as a well-known mark.
Here is an excerpt from the trademark act through which one can understand how the registry determines if a mark is a well-known trademark.
Section 11(6) in The Trade Marks Act, 1999
(6) The Registrar shall, while determining whether a trade mark is a well-known trade mark, take into account any fact which he considers relevant for determining a trade mark as a well-known trade mark including—
(i) the knowledge or recognition of that trade mark in the relevant section of the public including knowledge in India obtained as a result of promotion of the trade mark;
(ii) the duration, extent and geographical area of any use of that trade mark;
(iii) the duration, extent and geographical area of any promotion of the trade mark, including advertising or publicity and presentation, at fairs or exhibition of the goods or services to which the trade mark applies;
(iv) the duration and geographical area of any registration of or any application for registration of that trade mark under this Act to the extent they reflect the use or recognition of the trade mark;
(v) the record of successful enforcement of the rights in that trade mark; in particular, the extent to which the trade mark has been recognised as a well-known trade mark by any court or Registrar under that record.
To understand the a process of trademark registration refer this blog : Procedure to register a Trademark in India