When you are citing a statistic or another specific fact, a signal phrase is often not necessary. In most cases, readers will understand that the citation refers to the statistic or fact (not the whole paragraph).
Legislation, however, is not a popular solution when it comes to most Americans and the food they eat. Nearly 75% of Americans are opposed to laws that restrict or put limitations on access to unhealthy foods (Neergaard and Agiesta).
There is nothing wrong, however, with using a signal phrase to introduce a statistic or other fact.
Legislation, however, is not a popular solution when it comes to most Americans and the food they eat. According to a nationwide poll, nearly 75% of Americans are opposed to laws that restrict or put limitations on access to unhealthy foods (Neergaard and Agiesta).
Marking boundaries between your words and the source’s words
Establishing authority
Introducing summaries and paraphrases
Putting direct quotations in context