Refers to one's firmly held personal belief or conviction, often used in formal or public statements.
He stated his conviction.
In his policy speech, the prime minister indicated the direction of his policies.
The new mayor stated his convictions soon after taking office.
The chairperson expressed his views at the start of the meeting.
意見 is a neutral word for an opinion on a topic, whereas 所信 conveys a deeper personal conviction usually expressed in formal contexts.
general policy speech
Compound of 所 (place, basis) and 信 (belief, trust), literally 'where one's belief is based'.