Which of the following is a sign that a transaction may be suspicious?

All of the options provided reflect potential indicators of suspicious activity, making the choice of all of the above appropriate.

Frequent transactions below the reporting limit can be a red flag when individuals or businesses structure their transactions to evade detection. This practice, known as "smurfing," often involves performing several small transactions deliberately designed to stay under the financial institution's threshold for reporting to authorities.

A high volume of international wire transfers can also signify suspicious behavior, especially if the transactions do not align with the customer's known financial activities or business practices. Such activity might suggest attempts to move illicit funds across borders, avoiding detection by local authorities.

Similarly, large cash deposits made without a clear explanation raise concerns for financial institutions. Cash transactions, particularly large ones, can sometimes be indicative of money laundering or other financial crimes, especially when the source of funds is unclear.

Considering these factors together underscores the importance of being vigilant in identifying potentially suspicious transactions. Recognizing any one of these signs can provoke further investigation, and in combination, they reinforce the need for diligent monitoring and compliance with anti-money laundering protocols.