Its wrong livelihood if the investment advisor persuasively recommends the investment, i.e. actively attempts to get his clients to fund the weapons company. Since shareholders are owners of a company, the shareholders are carrying on a business of trading in weapons.
Its not wrong livelihood if the investor merely points out the features of the weapons investment to his clients. There is no need for the investment advisor to "recommend" the investment. Instead, the investment advisor merely needs to "inform" the clients of the investment and leave it to the investors to make their own choice.
For example. I have been asked to contact you about a new investment opportunity our company is facilitating for our clients. It is an investment in a new weapons company. The return on the investment is expected to be 50% per annum because there is currently a war between Portugal & Spain and the new company is contracted to supply its new technology to the Portugese regime. The Portuguese regime, which is backed by the USA, has entered into a contract for 10 years of supply. If you are personally interested in investing in this weapons company, you can apply through our company, which has the exclusive rights to organise the public offer.
However, it would always be wrong livelihood if such offerings were very common in the job. In reality, an investment company would know what type of industries their clients are willing to invest in because generally investment companies ask these questions when taking clients.
In other words, generally, probably the same investment companies & the same clients would would manage & subscribe to the public offerings of new weapons companies. It would be wrong livelihood to work for an investment company inherently connected to the weapons industry.
For a Buddhist practitioner, it would be dispiriting/disheartening to frequently be dealing in weapons investments. But if this occurred only one a year, then a Buddhist invest advisor could present the information about the investment while remaining detached from the job. As originally said, the investment advisor cannot "recommend" the investment. They can only "inform" a client about the investment and speak in a way that places the intention or motivation to invest upon the client.
The law of kamma/intention is something natural & determined by neurological psychology. As said, for a Buddhist practitioner, it would be dispiriting/disheartening to frequently be dealing in weapons investments; even if the Buddhist tried to merely "inform" the client.
In Buddhism, there is a story not spoken by the Buddha about a hunter's wife who was partially enlightened. Personally, I do not agree with his non-Buddha story the hunter's wife might perform her duties cleaning the traps and such without blame of killing; because the Buddha taught husbands & wives should share the same morality. If the hunter will be reborn in hell for hunting, it is unlikely an enlightened wife would not exercise compassion & try to change her husband.
In the Pali scriptures, there are at least three teachings required to consider this matter:
Monks, a lay follower should not engage in five types of business. Which five? Business in weapons, business in human beings, business in meat, business in intoxicants and business in poison.
Intention, I tell you, is kamma. Intending, one does kamma by way of body, speech & intellect.
And what is the root of the unwholesome? Greed is a root of the
unwholesome; hate is a root of the unwholesome; delusion is a root of
the unwholesome. This is called the root of the unwholesome.