The City watchdog does not allow regulated firms to use its logo on websites or any form of documentation.
But Phil Bray, founder and director at The Yardstick Agency, warned financial advisers were still using the logo on their website, in breach of the rules.
The FCA has confirmed the use of its logo is prohibited and instead suggests a firm demonstrate its association with the watchdog by disclosing in writing it is "authorised and regulated by the Financial Conduct Authority".
Most firms also signpost their FCA number which can be used to search for a business on the regulator's register.
Mr Bray said it was "only natural" much of the marketing used by advisers and planners would centre around establishing trust with prospective clients.
"There are many ways to do that from publishing the results of client surveys to displaying client videos on their websites," Mr Bray said.
But he added: "However, we’ve seen a handful of firms display the FCA’s logo on their website, presumably as a way of communicating to clients and prospective clients that they are suitably regulated.
"It’s a laudable and understandable aim. However, the FCA does not allow their logo to be used in this way.
"I wouldn’t want any advisers or planners to fall foul of the regulator, so recommend that if they’re using the logo that they take it down."
The current FCA logo has been in use since April 2017 and cost more than £66,400 as part of a brand refresh.
High-end advertising firm Saatchi & Saatchi was paid a total of £57,600 to audit and design the latest logo and the FCA spent an extra £8,810 on designing the templates for the new brand and trademarking.
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