Police have issued security advice after "suspicious packages" were sent to a Scottish MP, a council building and the SNP's headquarters.
Officers said the "white powder type substance" was delivered between 25 and 26 April.
They said the packages were "associated with the forthcoming UK general election".
Officers were called to Mr Nicolson's office in East Dunbartonshire on Tuesday afternoon, while emergency services attended at Angus Council's municipal buildings in Forfar on Wednesday.
Police advice has been sent to all elected representatives across Scotland.
The guidance includes actions that MPs, MSPs, councillors and their staff should take if suspicious mail is received at their offices.
Assistant Chief Constable Wayne Mawson said emergency services were also responding to reports of suspicious packages delivered to the Scottish Police Federation building in Glasgow and to the Association of Scottish Police Superintendents based at the Scottish Police College, in Tulliallan, Fife, on Thursday.
He said that at Tulliallan no dangerous or noxious substance was involved and emergency services had been stood down and that inquiries were continuing the other incident.