Shinawatra was convicted in absentia on graft charges in 2008 and refuses to serve a two-year jail term, insisting the verdict was politically motivated by his powerful enemies.
The image circulating widely in Thailand's social media on Tuesday had a blunt message: "Welcome home big swindler Thaksin Shinawatra".
The image of a billboard next to a highway summed up the anger felt by many Thais about the prospect of the fugitive former prime minister returning after Sunday's landslide election victory by the party he controls from self-imposed exile.
The billboard was first erected in 2008, with a message welcoming Thaksin home after he was toppled in a coup, but it had now been doctored with the words "big swindler" inserted and circulated on the Internet.
The original message and the doctored version illustrate how split Thailand is on Thaksin, a 61-year-old telecoms billionaire adored as a populist hero by millions of rural poor but loathed as a corrupt, crony capitalist by urban middle classes, powerful generals and conservative elites.
He was convicted in absentia on graft charges in 2008 and refuses to serve a two-year jail term, insisting the verdict was politically motivated by his powerful enemies.
But his sister, Yingluck Shinawatra, is on the cusp of becoming Thailand's first woman prime minister, following her Puea Thai Party's win on Sunday, and her brother's return has suddenly become Thailand's hottest and most contentious topic.
A five-party coalition is taking shape and economists are predicting near-term stability for Thailand, but they warn any move by Puea Thai to whitewash Thaksin and seek his return could be political suicide at this stage.
"It's not necessary to risk the stability and popularity of this new government," said Charl Kengchon, a Bangkok-based economist with Kasikorn Research Centre.
"We don't know what Puea Thai's plan is for Thaksin, but they seem to be aware of the importance of stability and will prioritise other things in the short term like rolling out economic measures and fulfilling their (campaign) promises." But Puea Thai's rural-based "red shirt" supporters, who were involved in deadly clashes with the army in Bangkok in 2010, see the election result as opening the door to their "saviour" Thaksin, who they believe will again help them improve their lives.
Thaksin has been in self-imposed exile in Dubai for three years and has said he would like to be home by December to attend his daughter's wedding and for the king's birthday.
Thaksin would be arrested and jailed if he returned without an amnesty. Puea Thai says its policy of reconciliation may include a general amnesty, but insists a Thaksin-specific amnesty has never been its policy.
But it cannot escape the issue and all sides of Thailand's political divide seem convinced it will be pursued.
Yingluck has been evasive on the subject, sticking to the party line that reconciliation and economic problems were its priority and the amnesty debate was for independent panels to decide. Thaksin said on Monday he had no plans to return and was happy playing golf in Dubai.
Tuesday's Bangkok Post quoted an unidentified Puea Thai Party source as saying the amnesty would be sought when it could guarantee a bill had enough support to be approved by parliament. It could take as long as two years, but was "worth the wait," the source was quoted as saying.
But not everyone will agree.
"Thaksin was too corrupt. We can't let him come back. I support a female prime minister, but not her," said Natchapon Akararojit, a student at Bangkok's Chulalongkorn University.
Thaksin's enemies are almost certain to try to thwart an amnesty. If the issue gains traction, it could spark protests by the "yellow shirt" movement that held mass rallies undermining two pro-Thaksin governments in 2006 and 2008.
Moves are already afoot by another anti-Thaksin group to keep the powerful Shinawatra family out of politics.
Its leader, Tul Suttisomwong, has filed a complaint with the Department of Special Investigation accusing Yingluck of committing perjury in testimony she gave as part of an assets concealment case involving her brother three years ago.
Tul has admitted his motivation is to prevent Yingluck whitewashing Thaksin of his conviction.
"I'd like to make clear that I personally have no objection to any other Puea Thai leader assuming the premiership," Tul told Reuters. That view is echoed by many Thais, who view Yingluck as nothing more than a proxy.
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