First of all this company is innovative. Of course most companies pride themselves of being innovative. But the company committed to sustainable development embarks on a specific course of innovation - it continuously improves the quality, performance and profitability of its products and services while continuously decreasing their risks and impacts on the environment and society. It improves quality of life at the "power two". This is called eco-efficiency.
There is a second important sign. This company is preoccupied with the future of our world, not just the closer circle of customers, suppliers and investors. It integrates the trends and the weak signals of potential crises. In accordance with the values of the women and men that form it the company defines a strategy that ensure its profitability and also its responsibility in society. It does not favour one in neglecting the other even if this would be easier in the short term.
It is more and more a fact that these signs are not only appreciated by those close to the business, but also by the financial markets.

I would say the first sign is the actual taking into account of the interests at stake for all those involved with the firm. Sustainable development must ensure equitable respect for the interests of stakeholders, with a view to a long-term relationship between parties, thus promoting the implementation of truly durable policies.
The second sign, a consequence of the first one, is a serious commitment to verifiable transparency towards society - as opposed to mere promotional communication -, with regard to the company's aims and achievements. This alone will ensure a responsible relationship between stakeholders.
How? Through an independent and competent agency whose rating criteria are also transparent.